Clustered behind the small farms that dot the East Anglia tableland northeast of London are 84 of America's most valuable nuclear-armed pawns in the negotiating game that is being played between Washington and Moscow.

Barbed wire fences and wooden guard towers surround these pawns, known in arms control jargon as "forward base systems." They are, in fact, U.S. F111 fighter bombers stationed at Lakenheath Air Base, and they represent the biggest immediate problem confronting the ambitious goals that President Reagan outlined today as he boldly stepped into the Peace Game after a year of arms buildup and war-fighting rhetoric.

When Reagan's negotiators sit down in Geneva on Nov. 30 to try to sell the president's plan of an agreement that would lead to the dismantling of Soviet nuclear missiles targeted on Western Europe, the Russians are certain to say that such a proposal is impossible as long as those jets are at Lakenheath. The F111 would then be either the reason or the pretext for the negotiation's failing.

Each one of the swept-wing F111s flown by American pilots is ready to take off on 15 minutes' notice and drop up to 800 kilotons of nuclear firepower -- 64 times greater than the force that destroyed Hiroshima -- on a Soviet target. The F111 in Britain, along with the 56 aging British Vulcan bombers, contain NATO's primary long-range nuclear threat to the Soviet Union based on land in Western Europe.

But these planes are prey as well as potential hunters. They are almost certain targets for the even larger, nuclear-equipped Backfire bomber force that the Soviets built up to hit Western Europe if war comes. Paradoxically, Reagan's proposals on missile talks will inevitably lead to both sides having to focus on their medium-range bomber forces.

Reagan spoke in large part today to reassure Europe and to rebut the protesters who have taken to the streets across the continent to oppose the NATO plan to deploy 572 new Pershing II and cruise missiles.

Those protesters face a much different task in Britain. Ridding Britain of nuclear weapons means doing much more than keeping out cruise missiles or even removing all American bases. Here, it would require reversing the tide of Britain's entire postwar defense strategy.

That strategy is one cut to size for a declining world power that has chosen to put its faith in nuclear deterrence and response rather than spend nearly as much of its dwindling resources as it once did on a conventional military force to protect its interests. The cost consciousness of successive Labor and Conservative governments confronted with rising demands for public spending at home is a running thread through British defense policy for three decades.

The thread runs from the British decision of the 1950s to go nuclear -- a move that means Britain today is the only nuclear power besides the United States in the unified NATO military command -- down to the decision last year to spend $10 to $15 billion on the British version of the Trident submarine-based nuclear missile system. Until recently, the Trident decision has created far more controversy here than the decision to take cruise missiles.

Although the U.S. Air Force usually identifies only about a dozen major, actively used American bases in Britain, British Defense Ministry maps available to the press locate about 60 American bases and other facilities manned by about 25,000 U.S. military personnel throughout Britain. Other maps compiled by journalists and disarmament campaigners show more than 100 U.S. bases and facilities, some of them top secret, bristling with warplanes, nuclear weapons, spy planes, listening posts and communications networks.

Nuclear pacifists involved in the recent protest wave frequently charge that the island has become an unsinkable American aircraft carrier anchored off Europe. They assert that Lakenheath and the Royal Air Force base at Upper Heyford, where 72 other F111s are based, are almost certain targets for Soviet strikes if war breaks out.

An unspecified number of U.S. battlefield and tactical nuclear weapons for use by NATO troops in West Germany are stored in Britain. Much of the secret communications network needed to order and coordinate NATO nuclear strikes is located in Britain. Converted Boeing 707s are on an around-the-clock alert status at RAF Mildenhall, about five miles from Lakenheath, to serve as U.S. airborne command posts in wartime for the European theater.

"Plans for a future war assume that, if it should go nuclear, Britain could within one day suffer attack from 200 warheads each with an explosive yield equivalent to one million tons of TNT," notes Lawrence Freedman, head of policy studies at the Royal Institute of International Affairs and author of "Britain and Nuclear Weapons," a history that documents the eagerness of postwar British leaders to ally the country as closely as possible with the United States under a nuclear umbrella to deter attack on Britain's depleted military forces.

American strategic forces were first based in Britain in 1948 at the beginning of the Berlin blockade and airlift and were exclusively under U.S. command. It was not until 1951 that the British negotiated an agreement that the use of bases in Britain would be "a matter for joint decision between the British and American governments in the light of the circumstances at the time." That agreement will cover the 160 Tomahawk cruise missiles that Britain is taking onto its soil as part of the NATO deployment scheduled to begin in December 1983.

The "joint decision" agreement has been attacked by disarmament campaigners as permitting American bombers and missiles to be launched without British agreement under the pressures of an imminent Soviet-American nuclear exchange. British officials dispute such a contention, but decline to describe the extremely sensitive subject of whose finger gets on the nuclear trigger at which point.

"This is a matter of extreme sensitivity within the alliance at the moment," one NATO source said, citing possible pressures from other countries for a similar special agreement with the United States.

"The more fingers on the nuclear trigger, the less certain the deterrence," he noted.

Recent Soviet moves in the Peace Game confirm that Moscow sees the American nuclear-capable aircraft based in Western Europe, Greece, Turkey and on aircraft carriers -- the "forward base systems" -- as a particularly significant threat that has to be dealt with before any progress can be made on European nuclear disarmament. It is a problem that, in 1980, then-deputy secretary of state Warren Christopher called one of the most perplexing issues in the history of arms control.

During the first round of Strategic Arms Limitation Talks conducted by Henry A. Kissinger, the Soviets insisted that the forward base systems should be counted as strategic bombers, since they were under American control and could deliver nuclear payloads on the Soviet Union. Kissinger succeeded in keeping them out of the strategic totals covered by the SALT I treaty and the draft for a second SALT accord.

Now, in one of the most interesting moves on the negotiating chessboard since the shelving of the SALT II treaty negotiated by the Carter administration, the Soviets have begun to insist that the forward base systems have to be counted as part of the theater nuclear forces that are targeted on Europe.

This is the basis for their contention that the more than 250 SS20 medium range missiles that Moscow has deployed in the western part of the Soviet Union since 1977 do not disturb the nuclear balance of forces in the European theater. In their counting, the Soviets overlook the Backfire bombers they have deployed.

That is the argument that Soviet Foreign Minister Andrei Gromyko presented to Secretary of State Alexander M. Haig Jr. in a New York meeting in September, according to State Department sources.

That is the negotiating bedrock that U.S. representatives are likely to strike early in the Nov. 30 talks in Geneva when they try to launch Reagan's proposals for a trade-off of existing SS20s, SS4s and SS5s for cancellation of the Pershing and cruise deployment. Hours before Reagan went on the air in Washington today, the Soviet magazine New Times repeated the Soviet position on the forward base systems, dimming the chances that the talks will do anything other than stalemate early.

Even if the United States wanted progress badly enough to lump the fighter bombers in Britain into theater talks, it would have to take into consideration the likely reaction of British leaders, who have actively sought the deterrent value of having U.S. and British nuclear weapons for Britain's own national goals.

It is a presence that at times Britain has nurtured more carefully than has the United States.

Britain began research into atomic weapons early during World War II, submerging its efforts into the American Manhattan Project that produced the Hiroshima and Nagasaki bombs. But after the war, Labor prime minister Clement Attlee authorized development of a British atomic bomb, even though his government was strongly averse to its use. During the Korean War, Attlee warned then-president Harry Truman against using nuclear bombs in Korea, arguing they should be weapons of only the very last resort.

But later Conservative and Labor governments encouraged NATO alliance and British dependence on nuclear deterrence to bolster the prestige and cover cuts in conventional forces. This trend was made formal government policy by a Conservative defense minister, Duncan Sandys, in a 1957 White Paper that justified the ending of Britain's military draft and a drastic reduction of its conventional military forces by emphasizing Britain's commitment to nuclear weapons as the most effective means of deterring and, if necessary, fighting a war.

To lower defense spending from the 10 percent of gross national product it had absorbed during much of the 1950s, Sandys began what has since been a steady rundown of Britain's Army, Navy and Air Force. Sandys replaced cuts in personnel and equipment with less costly increases in nuclear armaments.

For example, Sandys reduced by 13,000 the strength of the then 77,000-member British Army of the Rhine in West Germany (which stands at 55,000 troops today) and halved the number of aircraft that would provide its air cover. But he said "This reduction will be offset by the fact that some of the squadrons will be provided with atomic bombs."

"It must be well understood," Sandys declared a year later, "that if Russia were to launch a major attack on the NATO countries even with conventional forces only, they would have to hit back with strategic nuclear weapons."

Although it remains committed to NATO consultation, the British government has maintained that its own independent nuclear force, capable of attacking Moscow, increases deterrence by forcing the Soviets to consider another "center of decision" besides the United States and France before launching a nuclear attack on anyone in the West.

At various times, British leaders also have regarded their own nuclear capability as an insurance policy against a U.S. refusal to use its own nuclear weapons, avoiding risk to American cities, to prevent the Soviets from overrunning Western Europe.

European officials say that the British nuclear force is reassuring to them as well. With British nuclear weapons at hand, the Soviets have to assume that an attack on the F111s could trigger a nuclear counterattack, even in the unlikely event that the United States would not want to risk trading Chicago for Lakenheath in a direct exchange.

"It just seems likely that you will only fire missiles when your own society is at state," a Dutch military officer said.

Britain agreed in 1962 to purchase a U.S. made submarine-based Polaris strategic nuclear missile system, for which the British built four submarines and the nuclear warheads. Rotating the submarines for repairs, the British always have one on undersea alert ready to fire 16 missiles each containing three clustered nuclear warheads with a range of 2,800 miles.

With the Polaris submarines scheduled for replacement in the 1990s, the Thatcher government decided last year to buy a new Trident submarine-based nuclear missile system from the United States. The British again would make at least four submarines and the nuclear warheads themselves. Constantly escalating cost estimates for this project range from $10 billion to $15 billion, which will be further inflated if Britain decides to buy the more advanced and expensive Trident II to which President Reagan has committed the United States.

This has made the decision very controversial on financial grounds alone for a country in economic crisis and a government committed to cutting public spending. Although the Thatcher government strenuously denies it, the cost of Trident is widely believed to be the reason for a scaling down of the Royal Navy announced this year, which has caused concern in the U.S. military about Britain's ability to carry out its responsibilities for defending vital northeastern Atlantic sea lanes in time of war.

Previously, the cost of Britain's independent nuclear deterrent had seldom exceeded about 2 percent of its total defense budget, making it far less costly than maintaining Britain's conventional defenses at immediately post-World War II levels. Now, Britain faces the greater cost of both a new independent deterrent as expensive as Trident and the increasingly expensive technological and labor costs of its conventional forces despite their declining size.

What worries critics like Michael Howard, an Oxford University historian and defense specialist, is the dependence of Britain and the other allies on the threat of first use of nuclear weapons to make up for falling so far behind the Soviet Union and the Warsaw Pact in conventional force strength.

"So long as the conventional balance remains uneven," he argued in a letter to The Times of London that has caused considerable debate, "the Western strategy of relying on the first use of nuclear weapons to defend ourselves is not only morally dubious but political and militarily incredible."

Howard faults both Western European governments for having refused since World War II "to take the necessary measures to provide for their own conventional defense" and the European nuclear disarmament movement for not calling for a strengthening of nonnuclear defenses to make this reliance on the nuclear threat less necessary.

"That is where the Campaign for Nuclear Disarmament is dangerous," Howard contends. "Their present campaign is sending a signal to Moscow and the United States, not simply that the peoples of Western Europe are not prepared to defend themselves with nuclear weapons, but that they are not prepared to defend themselves at all: a signal that could create a quite terrifying degree of instability by presenting the leaders of the Soviet Union with options that hitherto have been firmly closed to them."

Looking at the cost dilemma from a defense analyst's point of view, Christoph Bertram, director of the International Institute for Strategic Studies in London, said, "We have felt for a long time it would be desirable to reduce dependence on nuclear weapons, but the money for conventional forces -- the necessary increases in men and equipment -- has not been there."

U.S. and British sources insisted in recent conversations that they were only somewhat worried by the upsurge in nuclear disarmament sentiment here. They said they believed it still posed less of a threat to NATO than comparatively larger, more emotional movements in West Germany, the Netherlands and Belgium or the election of the new Socialist government in Greece.

But the British government and the American Embassy have become much more active in recent weeks in answering the disarmament movement with strong defenses of NATO nuclear strategy. Led by the foreign secretary, Lord Carrington, British Cabinet ministers have made a series of speeches warning of what they see as the dangers of unilateral nuclear disarmament.

"The government has no intention of becoming a silent and passive target for criticism of its defense policy," said Deputy Foreign Minister Douglas Hurd.