It was mid-May 1972, and the Kremlin Politburo was in a crucial meeting: President Nixon would arrive soon for a summit conference that the Soviets believed could yield a new superpower relationship involving major weapons agreements, wider trade, and perhaps equality, if not partnership, with the capitalist adversary.

Yet Nixon cunningly had just mined Haiphong harbor to complement intense aerial bombardment of North Vietnam, trapping 12 Soviet ships in side the mine ring cordon.

Should the summit be called off, as the Khrushchev-Eisenhower summit was canceled in 1960 after the U2 incident and the Johnson-Brezhnev summit after the 1968 Soviet invasion of Czechoslovakia?

Leonid Brezhnev, then as now general secretary of the Communist Party, architect of the Soviet opening to West Germany and Washington, polled the 14 other members. In turn, they agreed the summit should proceed. Only Pyotr Shelest, then 64, the Ukrainian party chief and anti-Western hard-liner, urged that the summit be canceled. He said Nixon was not welcome in the Ukraine.

"I won't shake a hand bloodied in Vietnam," he reportedly said.

Brezhnev turned to Vladimir Scherbitsky, a Ukrainian 10 years Shelest's junior added to the Politburo to buffer the older man's ambitions. "Do you agree with comrade Pyotr Yefimovich?"

"No, I don't agree," said Scherbitsky, according to authoritative unofficial accounts of the Politburo session. "The president is welcome in the Ukraine."

Now Brezhnev addressed Shelest. "You see, you can speak for yourself, comrade, but you can't speak for all Ukrainians."

That quiet statement sealed Shelest's fate and with it, the toughest voice of the hard-liners. Amid the Nixon visit, Shelest was quietly expelled from the Politburo and the summit formally ushered in "detente," the big-power formula for the 1970s.

The Soviet invasion of Afghanistan has again focused attention on the murky interior of the Kremlin for signs that hard-liners -- like the now forgotten Shelest -- have somehow ended the policy of detente upon which Brezhnev staked his leadership in 1972.

Inevitably, the assessment is tangled by outside events shaping and reshaping the hidden aims of government leaders. Much is known about the specific events. Very little is known about the thoughts of this particular set of leaders, 13 voting Politburo members whose average age is now above 70 and who rose to power through resilience, shrewd political judgement and brute force unchecked by any voice volunteered from the 263 million citizens they govern.

Only a handful of them have any personal knowledge of the West and none shares its values of democracy, law or individual freedoms. In viewing the world outside, they are guided by mixed expansionist aspirations and caution about security from outside attack that borders on xenophobia.

They see themselves directly threatened by China, with whom there have been sharp armed border clashes, and the capitalist countries, headed by the United States with its far-flung network of allies and foreign military bases.

From talks with official and other Soviet sources with some access to thinking within the Communist Party Central Committee, and with Western diplomats long practiced in measuring Soviet deeds against Soviet words, a picture emerges of the leadership's perspective while planning the Dec. 27 coup that installed staunch pro-Moscow leader Babrak Karmal at the head of Kabul's Marxist government.

Afghanistan had been foundering under the control of another Marxist, the headstrong, unpredictable Hafizullah Amin, who took power last September by killing the Kremlin's favored Afghan leader, Mur Mohammed Taraki.Soviet aid to Kabul since 1954 had topped $1.5 billion, far more than to any other country on the Persian Gulf periphery.

If the Marxist government fell, that Soviet investment would be lost and the West could be expected to move in following the Soviets' departure.

With the United States currently tied down by the hostages crisis in Iran, tactical conditions were ripe for Moscow to play out a favored policy -- applying force to gain absolute control of a fluid situation.

"Coercion is in the system, Soviet relations depend on control and they will use force when they need it to protect their interests," said one source, who cited the crushing of the 1956 Hungarian revolt and the 1968 invasion of Czechoslovakia. The Kremlin, it is said here, carefully took into account that in both cases, Western outrage had quickly died away and general relations were restored and improved.

For example, while the 1968 innvasion derailed the summit with Lyndon Johnson, it caused a delay of just eight months in Senate approval of the nuclear nonproliferation treaty, while talks resumed on strategic arms limitation after only a year's stall. For leaders who can expect to stay in power until they die or are incapacitated, and who are accustomed to wait patiently for conditions to turn in their favor, these are not lengthy intervals.

Soviet leaders apparently feel they are much stronger in almost every way than in 1968.Success in Angola and Ethiopia without great harm to bilateral relations was followed by the Soviet-backed Vietnamese invasion of Cambodia and defeat of the pro-Chinese regime of Pol Pot, with no interference from the West.

The Kremlin had successfully forged other close ties in distant places, such as South Yemen and Mozambique, making Moscow, in the words of a Soviet source, "an important force in Africa -- which they highly valued."

In Europe, trade with West Germany was booming. The 1975 Helsinki agreement on security and cooperation had satisfied Brezhnev's drive for legal recognition of Soviet hegemony in Eastern Europe. A new invasion could drive home to unruly neighbors like Romania an awareness that Moscow would never let its vital interests slip away.

In bilateral relations, the Kremlin saw SALT II already delayed and suspected the Americans were using the treaty as an attempt to influence the Soviets. "It had practically lost its meaning," said one Soviet. "How long were we supposed to wait while Carter increased his arms budgets?"

Trade with America had never come up to Kremlin hopes and the leadership concluded that sanctions would only add to the U.S. trade deficit since America is a net exporter to Russia.

With a hardening American attitude toward Moscow already emerging in the 1980 presidential campaign, buttressed by what are viewed here as concessions by President Carter to the U.S. military-industrial complex, both political and military detente seemed to have run its course.

In invading Afghanistan, the totalitarian leadership here could rely on inert Soviet masses, guided by propaganda, to go along. Soviet media do not show Russian troops in Kabul. Soviets in casual talks with Americans echo charges that the White House and CIA sought to establish anti-Soviet bases in fraternal Afghanistan. "In whose interest was it to do that?" a man remonstrated the other day.

The leaders who reached this decision are the same pragmatic men who turned to the West in search of other goals of the masses in the same direction. If they are now turning away, so will the people.

The military, directed by Brezhnev's protege, Defense Minister Dmitri Ustinov, is firmly under the control of the party in the view of analysts here. He might welcome the chance to test a new command cadre that soon will take over from the last of the World War II veterans.

Soviet armed forces are undergoing a massive technological upgrading under Chief of Staff Nikolai Ogarkov, a Central Committee member and strategic arms control expert whose chief patron is Ustinov.

While some here suggest there may be signs of tension detectable beneath the Kremlin's opaque surface, they seem too vague to decipher with any degree of confidence. Analysts and Soviet sources alike seem convinced that the Afghanistan invasion was the decision of a willing and unanimous show of hands. As Pyotr Shelest discovered, that is the way things are done in Brezhnevs Kremlin.