LONDON — BRITAIN is expecting to come under pressure from the United States to reduce its independent nuclear deterrent in line with the deep cuts ordered by Presidents Bush and Boris Yeltsin at their summit meeting in Washington earlier this week.
But although government officials privately concede that the pressures are likely to grow in coming months, Malcolm Rifkind, the British defense secretary, has indicated that the government is determined to nearly triple the warhead capacity aboard its fleet of missile-firing submarines.
British strategic analysts say the country's planned fleet of four Trident submarines will give it a nuclear capability well beyond any conceivable defensive need, now that the threat of international communism has receded.
Professor Laurence Martin, director of the Royal Institute of International Affairs and a leading authority on nuclear strategy, said: "Russia and the United States are moving into a world in which they are de-emphasizing the need for nuclear weapons.
"There will be a problem over whether Britain, as one of America's foremost allies, can go on maintaining a deterrent with no really plausible utility."
Professor Martin added: "The Americans, who are supplying the Trident missiles, are now talking about collaborating with our former target, and that poses further serious questions."
Britain finds itself out on a limb in relation to this week's Bush-Yeltsin agreement to slash their nuclear arsenals by two-thirds over 10 years partly because of the long lead time required to build nuclear submarines, and partly because of domestic economic problems.
The existing fleet of four Polaris missile-firing submarines is being phased out. But HMS Vanguard, the first of four Trident submarines, was launched as recently as last March.
The full fleet is unlikely to be in service until the turn of the century.
IN addition, the submarines are being built in British shipyards, and the government is reluctant to modify the Trident order because that would mean the loss of thousands of jobs in a shipbuilding industry that has been under severe pressure for more than a decade. If, for example, the government decided not to build a fourth Trident submarine, up to 4,000 jobs would be lost.
Mr. Rifkind greeted the news of the Bush-Yeltsin arms agreement with a brief broadcast statement indicating that work on the Trident fleet would go ahead on schedule.
Defense officials said Britain had been fully consulted before the summit. The officials maintained that the deal struck in Washington would have little impact on Britain's independent nuclear deterrent.
The officials acknowledged however that Britain is now the only country with plans for a significant increase in its nuclear arsenal.
According to the London-based International Institute for Strategic Studies, the aging four-boat Polaris fleet is capable of carrying 64 missiles, each with a range of 2,875 miles, and three Cheveline warheads - giving a maximum of 192 warheads.
The four Trident boats will also have 64 missiles, but each missile will have up to eight warheads, and unlike those aboard Polaris, the warheads will be independently targetable. Missiles will have a range of 6,062 miles.
The Trident fleet will have a planned operational life of 25 years. Each boat is expected to cost around $1.1 billion, and British defense officials say that a high proportion of the Trident construction budget has already been spent. This means that a scaling down of the four-boat fleet would not mean significant financial savings for the government.
John Major, the British prime minister, has defended the decision to continue the Trident program on the grounds that future political developments in the former Soviet Union remain unclear.
Before the April 9 general election he denounced opposition Labour politicians for suggesting that the Trident fleet should be canceled.
"It is far too early to be certain about future strategic threats. It is better to remain cautious," Mr. Major said.
Professor Martin, however, considers that some aspects of this week's Bush-Yeltsin missile deal will create problems for Britain.
"I am less worried about the number of warheads involved than about the psychological problem of justifying a deterrent force designed to operate in an era that appears to have passed," he said.
Privately, British officials concede that the agreement by the US and Russia to examine the feasibility of a joint global strategic defense system could undermine Trident's credibility as a deterrent.
They say the American Global Protection Against Limited Strikes (GPALS) research program, if fully implemented, would be capable of knocking out a nuclear force such as Britain's. If the US shared GPALS technology with Russia, the rationale of continuing to maintain a Trident fleet would be dubious.
British government sources said that much of the pre-summit consultation between Britain and the US had been about the implications for the Trident program of possible collaboration on GPALS between Washington and Moscow.