Mr Clinton said: 'If these nations join us in observing this moratorium, we will be in the strongest possible position to negotiate a comprehensive test ban and to discourage other nations from developing their own nuclear arsenals.'
The decision, made under pressure from the US Congress, represents the biggest step towards a full test ban in 30 years. However it is a setback for the British government, which will now be unable to carry out three planned tests beneath the Nevada desert. A 1,000ft hole had already been dug at the test site for the first of the series.
Speaking in his weekly radio address, Mr Clinton said the US would refrain from testing until October next year. 'If, however, this moratorium is broken by another nation I will direct the Department of Energy to prepare to conduct additional tests.'
The five nuclear powers are already observing a moratorium on testing which began when France announced last year that it was suspending its tests at Mururoa in the Pacific.
Whether they will all now accept a further moratorium is uncertain. Britain cannot test while the Nevada site is closed, and Russia wants a comprehensive ban, but China's plans are unknown and the new centre-right French government is under strong pressure to renew underground testing.
Malcolm Rifkind, Secretary of State for Defence, made clear Britain was 'concerned' that nuclear weapons should have the 'highest possible level of safety and reliability'. But British ministers insisted yesterday that, although the decision was a setback, it was neither unexpected nor disastrous. Other senior defence sources said it would not affect the strategic Trident programme, which had already been fully tested.
The most likely impact is on development of the replacement for the WE177 free-fall bomb - probably by a sub-strategic nuclear war on some Trident missiles.
With that option closed, at least temporarily, Britain will now be pressing the US for aid and assistance in developing alternative computer modelling and simulated testing techniques - in which the Pentagon is more advanced than the MoD.
Ministers also suggested that the Clinton announcement could stimulate closer Anglo-French co-operation on the development of nuclear weapons.
There is some scepticism in Whitehall that the decision will stick - first because the Chinese may go ahead with early tests, and second because congressional opposition to testing could still be reversed.
For some years, all nuclear testing has been done underground. China was the last to test in the atmosphere, in 1983.Reuse content