De Niro and Pacino. No contest

Big Bob and little Al. What a pairing. The masters of grunt, fidget and shrug do the Method thing in Heat: one's the good guy, one's the bad guy, but how else can you tell them apart?

Michael Mann's brilliant new urban action film, Heat, brings together for the first time Al Pacino and Robert De Niro, two of the greatest living exponents of Method acting. Perversely, Mann only gives them one scene together, when they mouth worldly-wise tough-guy cliches at each other, but it is De Niro, with a fresh, controlled performance as a coolly analytical and efficient robber, who comes away with the acting honours.

Pacino's enjoyable, charismatic, but over-the-top performance as a nervy, obsessive, relentless cop demonstrates yet again that the Method, the naturalistic style of acting said to have brought a new realism to performance over the past 40 years, can be as stylised and artificial as any which preceded it. It is a demonstration that is reinforced by De Niro's pallid, going-through-the-motions performance in Martin Scorsese's forthcoming Casino, especially in scenes with Method-victim Jo Pesci, whose narrow range reduces every scene he's in to inarticulate, aggressive bluster.

De Niro and Pacino both studied with Lee Strasberg, who adapted Stanislavsky's acting theories to his controversial Method in the early Fifties. Stanislavsky's view was that good acting should be true to life, thus encouraging spontaneity, improvisation and introspection. The result has been decades of fidgety, mumbling, inarticulate, self-conscious performances by intense but third- rate actors.

For much of their careers, De Niro and Pacino have shown what the Method can achieve. In their early films, introspection for both actors became immersion in the characters they were playing. "Some actors play characters," Strasberg once said, "Al becomes them." De Niro's immersion is legendary, whether he was wearing Al Capone's underwear for authenticity in The Untouchables or learning to play saxophone for New York, New York. He took it to its furthest extreme when he tucked in to massive amounts of pizza and ice- cream for a couple of months to play Jake Le Motta's run to fat in the second part of Raging Bull.

Both men regard themselves as actors rather than film stars - the difference being that actors play characters, stars play themselves. But acting in lead roles in Hollywood films is star acting, whatever the style of performance. And over a long film career, the difference between actor and star dissolves. Actors become stars through repetition, playing the same character over and over, exhibiting the same attractive or charismatic traits.

De Niro and Pacino share a capacity for brooding silence and explosive violence. Pacino has been at his best playing nervy rebels on either side of the law (Dog Day Afternoon, Scarface, Serpico, Sea of Love). De Niro has probably the broader range but, like any miscast old-style Hollywood star (John Wayne as Genghis Khan, anyone?), both have come unstuck when they have strayed too far from their personas. De Niro can't easily play humour (We're No Angels was a disaster), and both actors have come croppers in historical pieces (The Mission and Revolution).

With age - De Niro is 51, Pacino 55 - both actors are going easier on themselves. De Niro is making more films to subsidise his Tribeca film centre so has little time for deep research. Pacino has learned to "turn it on and off". "When you've been doing things for a long time it gets easier," he says. "You just walk into the character and when the shot is over you step out of it."

Sometimes this means that the two actors give performances or parts of performances the audience has seen before. It's hard to say whether this is because we are familiar with all their moves or because they are lazily falling back on stock mannerisms. But when Pacino in Heat suddenly shouts certain phrases very loudly totally at random to show how quirky his character is, you recall him doing it in Scent of a Woman and the way that might have developed from Michael Corleone's sudden outbursts in the Godfather trilogy.

Pacino also favours the common Method technique of gazing blankly off screen as a way of looking into himself. Doing this allows the audience to read into his blankness whatever emotion we think he's feeling. A cynic might say we do the work, his acting gets the credit. He has expressive eyes. "You got cop's eyes," someone says to him in Sea of Love and when in doubt he's not above just turning on his unblinking stare. He also drops fluidly into live-wire mode - a pop-eyed, fast talking, lip-smacking, high -strutting cocky character, equal parts Scarface and the short-order chef in Frankie and Johnny.

Although he seems to do an unusual amount of running in his movies - fast too, his short legs pumping, elbows well tucked - he's not a physical actor in the way De Niro is. Although bandy-legged, De Niro has used a variety of walks to express character. (In Heat he's lithe and brisk.) He adopts different postures for different characters but he also has a range of gestures for all purposes. Shrugs, hands held palm outwards and a stabbing finger that wouldn't look out of place in a silent film, usually accompanying the announcement, "I want him dead!"

De Niro, when not reined in, has several mannerisms. He has a standard hearty but dead laugh which he uses for dysfunctional characters in Cape Fear, King of Comedy and GoodFellas. The coarse grimace he first used while mugging desperately in We're No Angels - the one where he frowns and seems to be smelling something bad - crops up again and again in recent films to express distaste or anger.

His most obvious mannerism is his inarticulacy. In the Method, inarticulacy is a conscious tool for helping performers create an illusion of real behaviour. De Niro, pretty inarticulate in real-life interviews, has made it the highest form of expression. "A grunt can do more than a paragraph of text," he is quoted as saying.

Unfortunately, and especially in his collaborations with Scorsese, this inarticulacy too often becomes cliched and parodic. A typical De Niro exchange will have him repeating the same line in slightly different ways. ("You talking to me?" in Taxi Driver may have been an improvisation but it was a rehearsal for the same thing in almost any Scorsese-De Niro project). He will repeat the lines of the person who is talking to him. ("You're asking me what I'm doing? You're asking me? Let me get this straight - you want to know what I'm doing?" and on and on...)

These mannerisms occur so often we come to expect them, even enjoy them. De Niro once remarked: 'I don't like that Gone with the Wind type of acting. Clark Gable was a good actor but he always played himself. Humphrey Bogart just plays Humphrey Bogart." But, frustrating as it might be for them, by now that's exactly what De Niro and Pacino do. And when they have their short moment together in Heat the audience is aware at that point not of the characters they have immersed themselves in but of two great actors relishing their scene together.

n 'Heat' is on general release from 26 January

Lee Strasberg's post-Stanislavskian Method was designed not so much to enhance actors' technique as to put them in touch with their own emotions, as a means to express the innermost feelings of their characters. Here, then, is your at-a-glance guide to the big Hollywood tics and what they signify...

MARLON BRANDO

The Godfather of Method, fetishised fidgeting and odd 'business'. Rummaged for earwax during the love scene in One Eyed Jacks.

JACK NICHOLSON

Manic leerer. Eases neck in collar to act embarrassment or impatience; does 'slack-mouthed imbecile' to register surprise.

GENE HACKMAN

Another collar-clearer, which he amplifies with tilted head and jutting chin when miffed. Nervous, throaty snicker quintessential.

RICHARD GERE

Self-regarding walk is key. Trademark look, featuring clenched jaw and pout, is good for showing hurt, lust, anger, sorrow and petulance.

JODIE FOSTER

See Gere for narrow range of facial expression. Note additional flaring nostrils. Hence hallucinatory scenes together in Sommersby. MERYL STREEP

Accent as mannerism. Also: stammer, lateral eye movement, nervous, tight smile with tearful overspill. Can blush/ pulsate on demand.

MICHAEL MADSEN

Ask him a question, he sniffs, squints, looks down, smiles to himself, rubs face with finger and may or may not reply. '90s fidget king.

JESSICA LANGE

Rage, tears. That's about it.

HUGH GRANT

Only British Method great. Stutters, pushes back hair flop, grins unexpectedly, shoves hands in pockets, stoops suddenly and so on.