The London station of the Soviet KGB was placed on extraordinary alert in early 1981 by a Moscow directive stating that the United States was preparing to attack the Soviet Union, according to informed accounts of statements by the most valued British double agent ever to defect from the U.S.S.R.

According to informed sources, Oleg Gordievsky, whose defection after a dozen years as a British double agent inside the Soviet KGB was disclosed last September, told debriefers in London and Washington that KGB agents in Britain were instructed to gather every scrap of information that might bear on the supposedly impending U.S. onslaught.

Gordievsky was reporting an intelligence alert, as distinguished from a regional or global military alert. A military alert would set in train movements of Soviet forces visible to Western spy satellites and other intelligence resources. No evidence of any military moves related to this intelligence alert was detected in the West, sources said.

Headquarters of the KGB ("Komitet Gosudarstvennoe Bezopastnosti" in Russian, or committee for state security) on Moscow's Dzerzhinsky Square, according to Gordievsky's account, gave no explanation to its startled agents in London why, how, where, or in what magnitude the attack would come. KGB operatives in London, Gordievsky reportedly has said, considered the stark directive to be overreaction to the unpredictable, muscle-flexing new administration in Washington. But no nation's agents can debate with the control center.

The key words in the 1981-83 directive, as identically related by British and American sources, were that the United States was "going to attack" the Soviet Union.

It is not known if these sources were quoting from the Gordievsky debriefing transcripts, or were paraphrasing what they know. There are many blanks in the Gordievsky sequence, and dozens of questions about it. For example, it could not be learned when Gordievsky told his British handlers about the 1981 order, or whether -- if they knew of it in a timely fashion -- the British informed the United States right away, or only much later.

Gordievsky, a KGB agent since 1962, was first recruited in 1972 as a double agent when he was stationed in Copenhagen, where he served two tours of duty. He was assigned to London in 1982, became deputy chief of the KGB station there and in June 1985 was promoted to station chief.

The British government and the Reagan administration have declined to make any comment on the information in this article or even discuss what was disclosed in London about Gordievsky earlier.

The directive received in London, by Gordievsky's account, was neither a momentary bureaucratic bungle nor a fleeting alarm inside the world's largest espionage and secret police agency, then headed by Yuri Andropov. The order remained in force, Gordievsky reportedly said, through 1982 and until the end of 1983, when it was lifted without explanation.

While the order was in effect, on Nov. 12, 1982, Andropov became the surprise successor to the long-ailing Leonid Brezhnev as general secretary of the Soviet Communist Party, the first former KGB chief ever named Soviet leader.

From 1981 to 1983, Gordievsky reportedly said, special watches were mounted on all activities of conceivable relevance to the supposed U.S. threat: movements of VIPs, U.S.-British meetings, senior officials' limousine traffic. Everything was reported to Moscow in the intelligence sweep -- including a blood drive by the Greater London Council.

The Washington Post has confirmed a story first pieced together by BBC-TV reporter Tom Mangold and broadcast last November that Gordievsky made a sensational escape from the Soviet Union last summer, literally under the nose of the KGB, just after he was promoted to station chief and was recalled to Moscow, evidently under Soviet suspicion.

Admiring British and American intelligence experts describe the "exfiltration" of Gordievsky by Britain's MI6 as an operation as imaginative as anything in cloak-and-dagger literature. MI6 chiefs, it is said, assured Gordievsky that if he signaled from Moscow that he was in danger, all the resources of Her Majesty's Government would be drawn on to extricate him -- a promise that they fulfilled.

Britain's previously most renowned double agent inside the Soviet system, Col. Oleg Penkovsky, whose information was shared with the United States, was given similar assurances under similar circumstances in 1962 when he risked a recall to Moscow. As Gordievsky well knew, the British government's inability to make good on that commitment to Penkovsky cost him his life.

The 1962 "exfiltration" scheme involved a mock mobile trade exhibit led into Eastern Europe by Penkovsky's intermediary and courier, British businessman and intelligence agent Greville Wynne. Both Penkovsky and Wynne were caught. (Wynne was released in a spy swap in 1964.)

MI6 is said to have been much more imaginative in the Gordievsky case, and even hoped to extricate Gordievsky's wife and two daughters, whom he left behind. Sources said the plan involved transporting Gordievsky by land, air and sea, but details of his escape are still top-secret. American intelligence experts suggest that the escape may still be confounding a furious KGB, and if so could be usable again in some form.

The 47-year-old Gordievsky has been under "deep cover" since his double career was disclosed in London last September. The immediate rebound was expulsion of 31 Soviet officials and reporters from Britain, and the reciprocal expulsion of 31 British officials and reporters from Moscow.

The British are known to consider Gordievsky an unusual defector in many respects, not only for his lengthy service as a double agent. The British reportedly were impressed that Gordievsky had not broken with his homeland out of pique or for materialistic reasons, but sincerely came to believe that the Soviet system was wrong, and that his espionage work might help to change it.

Gordievsky, it has been confirmed in Washington -- as first reported in London's Sunday Times in November -- was a unique source of information in preparing President Reagan for his summit meeting with Soviet leader Mikhail Gorbachev in Geneva last November.

CIA Director William J. Casey, with the personal blessing of Prime Minister Margaret Thatcher, the president's close friend, met secretly with Gordievsky in Britain about six weeks before the Geneva summit, sources said.

Casey's prime interest then evidently was Gordievsky's firsthand knowledge of Gorbachev, his wife, and senior aides; their personalities, habits, idiosyncracies and operating style. As deputy KGB station chief in London, Gordievsky helped to prepare Gorbachev's visit to Britain in December 1984 -- three months before he became Soviet leader -- and worked with the Gorbachev party throughout its British trip.

Last February, it has been learned, Gordievsky was brought secretly to the Washington area for several days of debriefing by senior officials of the National Security Council, the State and Defense departments, and U.S. intelligence agencies.

Information acquired in those debriefings has been shared selectively with some senior officials of the Reagan administration, sources said, but even many high-level officials with extensive experience in East-West relations are still unaware of the contents of these debriefings, and even of the fact that they occurred. Informed sources said that few of the relatively small number of specialists in East-West affairs in the U.S. government have been fully briefed on Gordievsky's information. These sources questioned whether the administration has undertaken a comprehensive study of Gordievsky's information at the policy-making level.

Gordievsky's information is being analyzed in the National Security Council, the CIA, State and Defense, and other agencies, sources said. The level of attention being given to Gordievsky's reports, however, is markedly lower in Washington than in London and other Western capitals, where the most experienced specialists on the Soviet Union are said to be analyzing it with fascination for the light it may provide on the early 1980s, the most chaotic years in Soviet history in at least a generation.

Senior officials in the Reagan administration were operating on the premise, or conviction, that it was the United States that was being "tested" by a threatening, aggressive Soviet Union at the outset of its first term -- not the other way around.

Secretary of State Alexander M. Haig Jr. publicly called for "going to the source" of Marxist-suppported guerrilla warfare, and explicitly held the Soviet Union and Cuba responsible for what was happening in Central America. Haig wrote in his memoirs that he was attempting to shock the Soviet Union -- but not attack it or Cuba.

Soviet Ambassador Anatoliy Dobrynin, in his first meeting with Haig on Jan. 29, 1981, was not merely blocked from his privileged entry route into the State Department; he was bringing a Kremlin offer for a high-level dialogue pointing to an early summit meeting, which Haig rebuffed. In their first set of talks, Haig's memoirs relate, he read Dobrynin the riot act on Soviet global behavior, saying the U.S. priority was "an understanding on standards of international conduct"; the Kremlin especially "must control its client, Cuba" or "we would have to take action to protect our interests and our friends in the Western Hemisphere."

The Washington Post has previously reported that on three occasions during his brief tenure as secretary, Haig unsuccessfully pressed his colleagues in the administration to blockade Cuba with American naval vessels. The Soviet Union has troops and bases in Cuba, and warships and other vessels in the Caribbean, where the United States did mount a major show of force in the early 1980s.

At the same time, apart from Reagan's own challenging anti-Soviet talk, the secret guidance from Defense Secretary Casper W. Weinberger telling the U.S. military to prepare forces to "prevail" in a nuclear war became public, and a trillion-dollar buildup of American military power was under way.

In its own empire, the Soviet Union faced an unprecedented and volatile challenge in Poland. The decrepit Soviet leadership debated not only whether, but when, it dared risk invading Poland to suppress the workers' Solidarity movement and keep Poland in the Soviet camp as Washington repeatedly issued dire warnings about the consequences of a Soviet invasion.

Many senior administration officials scoff now, as they did then, at the suggestion that the Soviet Union was genuinely alarmed by U.S. military moves or public statements, or that Moscow had any justification for feeling vulnerable. The "war scare" in the Soviet Union in 1982-83 was deliberately engineered for propaganda purposes, these officials maintain -- a pretext to create a siege mentality in the Soviet Union, and to frighten the outside world about U.S. intentions.

America's allies, however, had apprehensions of their own about where the Reagan administration was headed, according to West European officials.

Many Western specialists, including some with access to Gordievsky's reports, attribute Soviet anxieties in the early 1980s to genuine apprehension about Reagan administration policy and a tactical decision to exploit that real concern, primarily for domestic purposes and only secondarily for external purposes.

Many analysts suggest that an important factor working on the Kremlin in those years was the maneuvering for position inside the Soviet hierarchy during Brezhnev's last illness (he died in November 1982), Andropov's illness, and his death in February 1984, Konstantin Chernenko's demise on March 10, 1985, and his succession by Gorbachev, a protege of Andropov.

The Soviet leadership referred in public -- in terms that baffled many Western officials -- to a grave international situation. On Nov. 7, 1983, for example, Politburo member and former Leningrad Communist Party boss Gregory Romanov -- who was to emerge as a major rival of Gorbachev in the struggle for leadership -- grimly stated in the Kremlin Palace of Congresses:

"Comrades, the international situation at present is white hot, thoroughly white hot."

Last February, Gorbachev told the 27th Communist Party Congress:

"Never, perhaps, in the postwar decades has the situation in the world been as explosive and hence, more difficult and unfavorable, as in the first half of the '80s. The right-wing group which has come to power in the United States and its fellow travelers in NATO have turned away from detente to a military policy of force."

Some Western analysts of the Soviet Union said alarmist rhetoric like Romanov's and Gorbachev's is more understandable in light of accumulating new information, including Gordievsky's revelations. One West European specialist with access to Gordievsky's debriefings offered this interpretation of Soviet behavior:

After years of acting on the belief that the United States under Presidents Richard M. Nixon, Gerald R. Ford and Jimmy Carter had acknowledged that the Soviet Union had achieved true superpower status, and expecting Reagan to conduct a foreign policy not unlike that of Nixon, the Soviets were caught off guard by the new Republican administration.

A series of hard-line statements and actions from Washington alarmed the Kremlin: the new administration's denigration of past arms control agreements or future negotiations; emphasis on development of a rapid deployment force that could be sent all over the globe; redeployment of mothballed battleships and then using one to bombard Lebanon; and more, all with the acquiescence of Congress.

There were also developments in American strategic policies that also caused Soviet concern: vastly increased budgets for weapons, authorization of deployment of MX missiles and development of Stealth bombers to penetrate Soviet airspace; new nuclear-armed Pershing and cruise missiles in Western Europe targeted on the Soviet Union.

Altogether, in this analysis, Moscow -- which traditionally operates on worst-case assumptions -- may well have seen the Reagan administration as not only determined to force the Soviets back from their hard-earned superpower status, but perhaps even to attack it.

Soviet alarm may have hit its peak in 1983, this analyst suggested, when Reagan unveiled his Strategic Defense Initiative, using such grandiose terms to describe it that Moscow may have concluded it was much closer to fruition -- and thus to a profound transformation of the strategic balance -- than Reagan would admit.

By 1984, this analyst said, Soviet panic had begun to fade. A careful second look revealed the complexity of SDI. Reagan himself abandoned fierce rhetoric and made overtures to Moscow, and calmer assessments began to come in from Soviet embassies abroad.

This specialist emphasized that his analysis was based on available information and his own hypotheses. Some other analysts in the West dispute the validity of any attempt to fill in all the blanks in Kremlinological reconstructions of the perceptions and actions of Soviet leaders.

In any event, veteran Soviet specialists said, the information Gordievsky brought to the West provides considerable raw material for new attempts to comprehend where the Soviet Union has been -- and where Gorbachev is trying to take it.

London correspondent Karen DeYoung and staff researcher James Schwartz contributed to this report.