Georges Marchais is one of those naturally combative politicians who much prefer to disagree with a proposition than to agree with it. He seems uncomfortable in the role that he has been obliged to play for the past two years: the responsible leader of a Communist Party seeking to acquire a respectable image by serving as a junior partner in a Socialist-led coalition.

During the past few weeks, Marchais has appeared to slide back naturally into his old role as the great irritant of French politics. Taking the central political controversy of the year--the deployment of a new generation of nuclear missiles in Europe--he has gradually moved from a position of appearing to support President Francois Mitterrand to sharply disagreeing with him.

At the same time he has managed to foster the impression that he is standing up to the Kremlin. During a surprise visit to Moscow earlier this month, Marchais made much of forcing the official Soviet news agency Tass to retract a news item reporting that he held "views identical" to those of Soviet leader Yuri Andropov.

"You know how intransigent I am," he boasted to French journalists on his return to Paris.

Political commentators believe that Marchais' principal aim has been to strengthen his grip on the Communist Party and rekindle the enthusiasm of rank-and-file activists disillusioned by the alliance with the Socialists.

The central fact to emerge from weeks of tortuous political maneuvering is that the French party now supports Soviet demands for the inclusion of French and British nuclear weapons in the Geneva talks on intermediate-range nuclear missiles.

Mitterrand's position, which is shared by the United States, is that French nuclear forces have no place in the Geneva talks. His reasoning is that the French missiles constitute a strategic deterrent under independent command rather than an intermediate nuclear force comparable to the Soviet SS20s or the Pershing II and cruise missiles that the United States plans to deploy in Europe beginning at the end of this year.

At first, Marchais seemed to accept this position--or at least he concealed his differences with Mitterrand in the interests of government unity. At a lunch given by the Anglo-American press corps in Paris in February, he insisted that the Communist Party fully supported the government's defense policy.

With the approach of the deadline for the deployment of American missiles in Europe, the Communist Party's position on defense has gone through what French commentators describe as an "evolution." It coincided with a series of statements by Mitterrand reaffirming France's commitment to the Atlantic Alliance despite France's withdrawal from NATO's integrated military command during the presidency of Charles de Gaulle.

As a pretext for his turnaround, Marchais seized on the joint statement, signed by Mitterrand and other western leaders in Williamsburg on May 29, that emphasized the "indivisible" nature of western security. Three days later, the Communist leader said that "after Williamsburg" France no longer could insist that it was not concerned with the negotiations in Geneva.

Driving his point home in a speech last week, Marchais said: "One cannot say to the Americans, 'You can count on us' and at the same time say to the Soviets, 'You don't have the right to count us in on one side or the other.' "

The closeness of the French Communist Party's new position on "Euromissiles" to that of Moscow appears to have been deliberately disguised by well-publicized reports of differences between the two sides. Most French specialists in Communist affairs echo the view of Michel Tatu, writing in Le Monde, who described the disagreements as largely artificial.

Marchais has gone to considerable pains to emphasize his support for maintaining France's independent nuclear deterrent at its present level. But, as the communique that he signed with Andropov in Moscow made clear, the Soviet Union is not asking for any reduction in French forces. What it wants is to be allowed to offset them with its own SS20s.

Mitterrand has responded to Marchais' challenge by taking every opportunity to repeat the official line. Questioned on the subject during a recent television interview, he said: "Everything concerning national independence and our territorial integrity will be decided neither in Moscow, nor in Washington, nor in Geneva, but in Paris, and by myself."

The Communists, however, have made clear that they intend to continue to press the issue. The party plans more "peace" demonstrations in the fall as a follow-up to a rally attended by 50,000 to 100,000 people in Paris last month.