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In the hills above Los Angeles the custodians of the J Paul Getty Trust have created a vision that blends academic institution with cultural theme park. But can the new Getty Center be both a picture palace and a people's palace, and would the oil magnate have approved of either?

FOUR MONTHS ago, on their first day at the Getty Center in Los Angeles, staff were asked to line up across the wide square in front of its vast half-built art museum. They were each given a pair of black sunglasses, safely styled and stamped with the Getty logo. It was soon apparent why. Nearly every morning, the southern California sun sweeps up over the Santa Monica mountains to the east, catches the Getty Center's ridge-top, and pours into its rooms like an office worker's curse. The buildings have walls of glass, portholes, pale paving and pale-painted halls; they suck the glare in until the sun sinks into the Pacific Ocean. The staff put on their sunglasses, and made small bitter jokes about Richard Meier, the Center's light-infatuated architect who comes from a cloudier part of the country. "Rats in a cage" became a favourite, muttered phrase.

The cage has since grown grander. The J Paul Getty Museum, one of the largest to be established this century, has risen as a castle of thick marble towers, hollow with galleries awaiting Rubens and Renoir. Around it clusters an idealised hill-town of cubes and half-towers: the Getty Conservation Institute, the Getty Information Institute, the Getty Education Institute for the Arts, the Getty Research Institute for the History of Art and the Humanities - a whole worthy alphabet of art- administering bureaucracy. Between the buildings, balconies jut out over Los Angeles; colonnades stand ready for strolling and contemplation; every surface is even or elegantly distressed.

And yet the Getty Center still jars. Partly, this is its newness: while the institutes are mostly occupied, the museum will not open to the public until December. Staff stand gingerly in the bright spaces, as if afraid to mark the surfaces. "Right now it's too precious and clean," says one manager, sitting in her fishbowl of an office. "It needs ice cream thrown on the plaza." From next year, the visits of school parties and professors should stain the paving to the shade expected of a serious museum; less easy to smooth away may be the suggestion of a certain hubris.

The Getty Center is as much an advertisement for its sponsors, the J Paul Getty Trust, as it is a place for the Trust's actual mission - "the diffusion of artistic and general knowledge", as its founding father decreed - to be carried out. Richard Meier's boxy designs form a billboard: marching along the very crest of their ridge, gleaming and angular against the soft dark folds of green and brown. Seen from the eight-lane freeway foaming below, the Getty Center echoes the Hollywood sign, announcing itself and its wealth to the infinite sweep of west Los Angeles.

But not everyone is impressed. "They're the big people up on the hill," says Mark Greenfield, director of the Watts Towers Arts Center, an hour to the south. "They make a big noise about doing work with communities. They don't do a lot." The Getty's neighbours have had their reservations too. The hills to either side of the Center belong to Brentwood and Bel Air, suburbs of well-pruned rose bushes, reproduction cottages, and expensively purchased city vistas. From this subtropical Surrey, shaded by the Getty in late afternoon, a stream of objections and delays to the Center's construction has issued forth ever since the project was mooted in 1984. The buildings cannot rise over 65ft; cannot include a campanile or visible car park; and cannot be purely white, which is Meier's signature colour. No fewer than 107 planning restrictions have been imposed as a result of local objections, the most for a single development in the city's history. The Center's cost has ratcheted up as its completion date has slipped: from $300m and 1991, to $600m and 1995 and, currently, $1bn and "a target" of the end of this year. "There were a few neighbours who were trouble," says Harold Williams, the Getty Trust's president.

Their fussing has a resonance, however. Fifteen years after it was established, the J Paul Getty Trust remains the hulking novice of the art foundation world. Its founder, Jean Paul Getty I, was an oil billionaire from Oklahoma with a hatred of modern art and an eye for antiquities. As he rose during the Thirties and Forties, making deals from phone boxes and charging his houseguests for their calls, Getty began buying up Greek vases and Renaissance paintings on his business trips. By 1954 his mansion in Malibu was full enough to show to the Los Angeles public. Getty's ambitions quickly widened: visiting Herculaneum, he became entranced by the ruin of a villa once inhabited by a friend of the emperor Hadrian. Getty imagined himself as a latterday Roman emperor; in 1974 a second Getty museum opened, also in Malibu, in a precise replica of the villa.

Art critics scoffed: the Getty was ostentatious, without style. In their eyes nothing changed after Getty died in 1976, and his Trust acquired $1.2 bn. The endowment has since swelled to $4.5bn, and with it the Trust's chafings against the rest of the art world - its attempted purchase of Canova's Three Graces, its out-bidding of the proudest museums. New patronage often seems domineering; what is unique about the Getty Trust is the scale and compulsiveness of its spending.

Every year, the Getty, which is a charity, must give away five per cent of its endowment - currently $225m, 10 times the budget of the National Gallery in London - or start paying taxes. Jean Paul liked to claim that he had never handed over more than $500 to the revenue service. But the Trust he established with a similar purpose in mind quickly encountered a snag: its cash, if spent entirely on art, would artificially bloat prices and alienate every other institution; ultimately, it would run out of masterpieces to buy. The Getty Center, with all its cost overruns, is the solution to this curious rich man's dilemma, written in marble.

BEFORE Harold Williams was put in charge of the Getty, he lived and breathed share prices as chairman of the US Securities and Exchange Commission. With his pulled-up baggy trousers and jowly, crafty smile, he suggests a Wall Street sage of the old school. His office is the width of a tennis court, looking north from the Getty Center at the traffic pouring through a distant gap in the mountains. He leans back in his black leather chair.

What exactly is the Getty Center for? Williams drawls cosily: "It's to ... " He stops. He bobs a little in his chair. The pause thickens; through the window, red tail lights stream by, far below. "... It's to enhance the activities of the museum and the various institutes ... " Twice as many paintings will be on display as were shown in Malibu. None of them, however, will be from the century or continent to which the Getty Center belongs. "We had enough on our plate trying to build a collection of western art," says Williams, smoothing away the strangeness of this restriction. "There's much to be said for letting the passage of time put some perspective on the timelessness of new art."

Caution at auctions, however, does not help the Getty Trust spend its money. "We do have more than most," Williams says, with something close to a shrug. "But go to the institutes and they will all tell you the wonderful things they could do if they had more money ... " Then, finally, he thinks of one himself: "We produce publications to a higher standard than many. We try to make sure the colour's right. We are rigorous."

The Getty Center, in fact, is close to rigid with self-affirmation and serious purpose. The directors of its departments nod at each other's statements, sound grave about budgets, recite their current and future projects like a mantra. "Monastic" is a favoured word - but this is a monastery with picture windows so visitors can see the order at work. "We want people leaving to say, 'We've just been to a place that has a mission'," says the press officer. Yet a sense of contrivance lingers. The decision to build the Getty Center preceded any definite ideas about what, apart from the museum, to put in it.

In Conservation, Miguel Angel Corzo talks very fast about his department's research into the relative effects of pollutants on paintings, its restoration of ancient human footprints in Tanzania, its protection of pieces of Jerusalem - in sum, its self-appointment as the guardian of the world's cultural treasures. Corzo smiles and bubbles and insists on a tour of his laboratories. "You can just flip and flop around here for days," he says, as he slaloms, suit flapping, though his caverns of blown-up slides and microscopes. Of one facility he is particularly proud: the meeting rooms. They stand, glass- walled, at the corners of each open-plan space. If any member of his staff needs one, they simply point their computer cursor, click once, and the nearest room will be reserved for the next half hour. "We needed to empower the staff," says Corzo. All the meeting rooms are empty.

THEN AGAIN, perhaps it is a mistake to look for a great academy at the Getty. For all the Center's archives and visiting scholars and distant plans for "an advanced studies centre comparable to Yale or Harvard", the grain of the place suggests something else - a theme park.

The Getty villa at Malibu draws 400,000 people a year. Most of them do not come for Mantegna, but for the fountains, the pools, the reproduction mouldings, the novelty of a rich man's fantasy - all the features that the art critics found so kitsch. The Getty Center has learnt this lesson too. Visitors first glimpse it from the freeway, a Disney creation in profile if not detail. A minute further on, a sign draws them off the road, to double back past the Center again. At the base of the ridge, an underground car park swallows them up. Lifts rise to the surface and a minimal railway station of the most unblemished white, like a tube stop designed by Mies van der Rohe. The train is driverless and electric; as it slides silently up the curving spine, the freeway reappears below, then the mansions of the Getty's neighbours, then the sunstruck grid of the city beyond, then, above and ahead, the approaching marble ramparts of the Center itself.

The Getty's appeal is simple: a day out with a gallery attached. Entrance will be $5 per car, or nothing at all - rare in America - for visitors by bus, bicycle or on foot. Picnics will be allowed, staring at the views encouraged, lounging about tolerated. There will be coffee stands, a restaurant with roasted vegetables and a rooftop view to the ocean. The idea, says Williams, is "keeping it light", in a city where the few public parks are usually anything but. And then, when the families are sun-sated and fed, they might just go indoors and look at some paintings.

"The landscape and views are a way to get the hook in the mouth," says John Walsh, the museum's director. He is tall and wears a special wood-effect hard hat. Walsh is overseeing the final construction of a new kind of gallery: for short attention spans. Each of its towers contains several high-ceilinged rooms, none big enough for more than half a dozen pictures. The towers are linked by walkways: some glassed in over a central courtyard, others open and seemingly hanging in mid-air over Los Angeles. Between paintings, the views are offered as treats; soon there will be another coffee stand to speed circulation, information and play areas too. Deep in the basement, for the most tired or persistent visitors, the modern austerity of Meier's rooms suddenly gives way to a fantasia of reproduction French interiors, all gold, mirrors and door handles like cherubs, copied from 18th-century Parisian townhouses. "The building," says Walsh, "has cues for the more unfamiliar visitor."

The pursuit of such an audience is a constant in the rhetoric of the Getty. "We want to reach out much more effectively into the community," says Harold Williams, suddenly animated in his Waspy tweeds, "into the diversity of Los Angelenos, who are not by and large museum-goers." Most likely, in a city that will soon possess a Hispanic majority, the diversity of Los Angelenos do not share Jean Paul's fixation with the finely wrought products of an alien society and time. The funfair aspects of the museum acknowledge this; so too, increasingly, do the activities of the Getty's institutes.

The walls of the Trust offices are hung with the kind of modern asymmetries its patron would have loathed. The Research Institute is studying the Fluxus movement, including the conceptual pranks of one Yoko Ono; the Information Institute is helping local "community artists" set up Websites; there is talk of contemporary sculpture at the Center - week by week, the old elitist notions at the heart of the Getty Trust are being busily outflanked. Only one Getty descendant, Gordon, remains a trustee. And even the new architecture defies Jean Paul: he built his Malibu villa as a statement against "one of those concrete bunker-type structures that are the fad among museum architects".

GLASNOST at the Getty can only go so far, though. Mark Greenfield's project is in a different Los Angeles altogether. The Watts Towers Arts Center, a small community gallery of the kind so regularly invoked from the ridge-top, was founded in 1956 as an addition to a freakish local landmark: a set of metal spires, wild as Gaudi and encrusted with tiles, obsessively erected by an Italian immigrant. Watts area was, and is, mostly black, dusty and poor; riots flamed though it in 1965 and 1992; the roads make cars judder. The Arts Center is just by the railway tracks, a single square building coated with murals and barbed wire. Its blinds are pulled tight against the sun.

Greenfield, a quietly muscular ex-policeman, would like the Getty Trust to help buy a house across the street so the Center can have an artist- in-residence. The Trust has agreed to publish a coffee- table book about the Towers; about the house, it is less keen. The Watts Center gets $70,000 a year from the city authority, plus a bit less from a supermarket chain, for its art classes, drum festival, and continuous exhibitions; its premises leak and have been temporary since 1970.

But Greenfield does not envy the Getty: "There's a certain underlying panic in the big museums," he says in his hot little office. "There's a whole generation of kids who've never been to a museum. They don't know how to behave: if you say, 'Don't touch that,' they still do." So far, the Getty Center has had money to shield it against the outside world. Its ridge has been terraced against winter landslides, any flammable plants uprooted against summer fires. It has self-sealing galleries, clever anti-earthquake joints, a half-million gallon water tank, an emergency helipad. Local critics like Mike Davis, a writer, have been offered research fellowships. He accepted.

Opening to the public will be less straightforward. Some staff worry about teenagers pressing up against their wide office windows - about the theme park co-opting the academy entirely. It is one thing to claim allegiance to a vast, unruly city, another to invite it in every day of the year. And if the panorama of Los Angeles is one of your major attractions, that too can be problematic. Near the end of my interview with Harold Williams, just as he was envisaging "the Getty putting LA on the map, culturally, for good", his phone rang. It was his wife. The latest OJ Simpson verdict was about to be announced. Williams still had to drive home; a tiny leap entered his voice.

Afterwards, on the Getty battlements, the security guards seemed to have gone. To the south, the sky was close to dark, a prism from black to brown to yellow and a sliver of the faintest blue. That was the way towards Simpson's courthouse in Santa Monica, and beyond it, Watts. The darkness was alive with the tiny lights of police helicopters.

! The Getty Center (310 440 7360) opens in December.