America wants to turn the unthinkable into usable tools of warfare

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Leading article: Behind the warm words of President Bush lurk some dangerous thoughts

Yes, it's only contingency planning, an exercise conducted by any self-respecting national defence ministry to confront "just-in-case" scenarios – what Colin Powell, the American Secretary of State, called simply "sound, military conceptual planning".

But as the heated reaction around the world yesterday proves, the leak of America's new thinking on nuclear weapons has far-reaching and, for some, frightening implications. To allay these anxieties, it will take a good deal more than the assurance from Vice-President Dick Cheney that America was not planning pre-emptive nuclear strikes against anyone.

Technically that may be so. But the Pentagon blueprint worries arms control experts on two scores. First, by urging new and less powerful weapons that create less fall-out, America gives the impression it is seeking to lower the nuclear threshhold, to turn weapons regarded as the unthinkable last resort of deterrence into usable tools of warfare.

In the dry language of the review, "greater flexibility is needed with respect to nuclear force and planning ... nuclear attack options that vary in scale, scope and purpose will complement other military capabilities."

As such, the ideas reconjure up the old notions of battlefield weapons and neutron bombs, criticised in their time for blurring the distinction between nuclear and non-nuclear weapons. Once even a small weapon had been exploded in anger, it was feared, nothing would stand in the way of the spiral to the most fearful weapons.

The reaction from directly interested parties was swift. Iran predictably claimed that the blueprint was further proof of America's desire to intimidate and impose its will on the rest of the world. China, one of the seven countries singled out, suggested that Washington wanted to return to the Cold War. One Russian politician acidly commented that since 11 September Americans "have somewhat lost touch with the reality in which they live".

The hypothetical new generation of weapons for which the Pentagon yearns would be able to take out specific targets, in countries that do not have nuclear arms (of the seven specifically mentioned in the review, Libya, Syria and Iran are known not to have nuclear weapons). The review would seem to reverse the long-standing American position that Washington will not use nuclear weapons against non-nuclear powers, unless they are fighting alongside a country which does have nuclear arms.

Diplomatically the adverse fall-out may be even more immediate. By refocusing on nuclear weapons that might be used, the overwhelmingly mightiest conventional military power seems to be undercutting its own efforts to prevent nuclear proliferation, increasingly the justification for President George Bush's war against terrorism.

Far from deterring proliferation, the leaked plans may make countries that have acquired nuclear weapons, such as Pakistan and India, more ready to use them, disarmament experts say. Countries believed to be pursuing them, such as North Korea, Iraq and Iran, are likely to step up their efforts.

America insists that the nuclear non-proliferation treaty is the best avenue to contain the spread of nuclear weapons. To encourage other countries to sign up, it pledged it would never use such weapons against a country that did not have them. That assurance has now been removed, at least by implication.