In the week since French President Valery Giscard d'Estaing returned empty-handed from his meeting in Warsaw with Soviet President Leonid Brezhnev, diplomats and commentators in Western Europe have been trying to divine what Giscard was attempting to achieve.

Most analysis leads to the conclusion that by breaking Western solidarity, Giscard was seeking to guarantee himself a reelection that has been looking at least somewhat questionable.

As Jean-Francois Revel, editor of the newsweekly L'Express, put it, Giscard bought "the discreet neutrality of the French Communist Party" in the 1981 presidential elections.

"It is the only key for understanding a diplomacy for which it is difficult to find any logical explanation from a strictly foreign-policy standpoint," Revel said.

While the permanent weight of the Communist Party in French politics seems to be at the root of Giscard's move, the long-term effects and implications on the West are incalculable. Some of the coolest heads in Europe warn that this could represent the real beginning of the "Finlandization" of Western Europe, the accommodation to Moscow the Soviets seek.

"If the Soviets meant to show what is the real state of the Western alliance, to explode all the myths we have been living by, then the invasion of Afghanistan could not have succeeded more brilliantly," said a veteran continental diplomat.

The reactions to Giscard's move also underline French ability to influence others in Europe and the Third World. It is an ability many Americans, even on the policy-making level, underestimate.

Giscard's apparent need to go to Warsaw to get communist support at home also suggests an answer to the nagging questions of why French governments since Charles de Gaulle, regardless of their intentions when they start out, have wound up having strained relations with the United States.

After the week pro-American Third Force governments of the 1950s that embraced everyone in the French political spectrum between the Gaulists and the Communists, De Gaulle worked out a new French national consensus based on the assertion of French "independence" between Moscow and Washington. The French Communists could only applaud because this involved loosening French ties with the United States.

It was the basis for a system of government that went far toward answering the basic dilemma of French politics: how can you govern by denying up to a quarter of the electorate a sense of belonging to the nation?

The Gaulist answer worked, at the price of granting the French Communist Party's Kremlin mentors substantial leverage over French political life.

The Soviets have been able to throw electoral clout to each of the three presidential winners under De Gaulle's Fifth Republic.

Yet De Gaulle also had a keen sense that the way to preserve the reality of French independence was to keep shifting France's weight to the side that looked as if it might weaken in the world power balance. He unhesitatingly leaned toward the American side in the Cuban missile confrontation and in the Berlin crisis. His place in French history was assured originally by his refusal to accommodate himself to the German domination of the continent in 1940.

Giscard's analysis is clearly that the United States has declined. His entourage makes no mystery of this. But the French president's answer is not the traditonal Gaullist one of urging the Americans to stiffen their spines. Instead, French diplomacy seems to seek ways to accommodate itself to ascendant Soviet power.

Despite all the hesitations and carefully shaded nuances, the original French position on Afghanistan was the basically tough one that there could only be a solution if the Soviets first withdrew their invasion forces.

Now, French Foreign Minister Jean Francois-Poncet is saying that there should be a summit meeting of the great powers next year "to define the conditions in which the Soviet Union could be brought to withdraw its troops from Afghanistan." The French minister said at another point last week, "Afghanistan must not become an armed camp against the Soviet Union."

This would give the Soviets a year to try to end the Afghan rebelion in their own way.

The Soviet ambassador in Paris, Stepan Chervonenko, one of the Kremlin's most important diplomatic spokesman, made clear after Giscard's return to Paris how Moscow conceives the political settlement that the French leader said he senses that Brezhnev seeks.

A unilateral Soviet withdrawal from Afghanistan, Chervonenko said, would be "a gift to the United States" and would guarantee the continuation os "foreign interference in Afghan affairs."

Soviet withdrawals, the ambassador said, should be preceeded by the diplomatic recognition of the Soviet-imposed Afghan government, by "recognition of the irreversibility of the democratic Afghan revolution," and by noninterference in the future.

Chervonenko intimated that France can help the cause of peace and detente even more by using its influence to help China and Pakistan see reason.

The Soviet ambassador then hailed Giscard as the worthy successor of De Gaulle and the continuer of his policies. That was that last straw for many Gaullists.

Jean de Lipkowski, Gaullist leader Jacques Chirac's foreign affairs adviser and a former deputy foreign minister, said that Giscard's foreign policy "has nothing to do with Gaulism, which was an overall analysis of great changes of balances in the world." Comparison of Giscard's policies of accommodating the Soviets to Gaullism was "indecent," he said.