A French diplomat once achieved great success with an elaborate novel called "La Grande Conference," about a major international meeting in which the maneuvers, personalities and interrelations of the participants were described in minute detail, but the author never said what the conference was actually about.

To many of the participants here during the last 10 weeks of the preparatory and opening meetings of the current Conference on Security and Cooperation in Europe, it has sometimes seemed that they were so lost in the thickets of Soviet-induced procedural debate that real life had become a replay of the fictional Grande Conference.

Yet, the real stakes involved a decision by the Soviet Union and is major European allies on whether they have already collected about all they can reasonably expect from the process of political detente, and have therefore become immune to Western pressure for more internal liberalization.

Getting at least the beginning of an answer on the eve of the Reagan administration's arrival has a major importance.

Western diplomats widely believe that the Soviets could afford to engage in these weeks of haggling because they got what they really wanted from the 1975 Helsinki accords the day they were signed. That is the consecration of the post-World War II boundaries giving them effective control of Eastern Europe.

In exchange, they committed themselves to a series of human rights principles already largely embodied in the 1936 Stalin constitution and the United Nations Charter, none of which noticeably hindered their previous actions.

Before the Soviets finally accepted yesterday a last-ditch agenda compromise effort by Europe's neutral nations to save the conference, even some of the U.S. delegates most dedicated to the spirit of Helsinki were admitting to serious doubts about whether the West had struck much of a bargain in 1975.

"What the Soviets got," admitted Max Kampelman, cochairman of the U.S. delegation, "they put in their pockets long ago. What we get, we have to correct as we go at every meeting like this one."

The Soviets showed themselves to be capable of accommodation. But when they did, questions were raised about what they had in mind.

Soviet Deputy Foreign Minister Leonid Illichev endorsed an often-repeated Western concept, "the indivisibility of detente." Westerners use it to mean that the Soviets cannot do anything they please in Afghanistan, for instance, and expect relations to be unaffected in Europe.

In Illichev's terms, however, it seemed to mean that Westerners cannot expect to get away with criticizing the Soviet civil rights record or Afghanistan and not have to pay a price in other fields.

As a Polish delegate with lots of Western contacts at the conference put it: "All this talk about Afghanistan is not very helpful. It is bound to create procedural difficulties."

President Gerald Ford went to Helsinki in 1975 to sign the Final Act negotiated under his secretary of state, Henry Kissinger. He apparently reasoned that little or nothing was lost by giving purely legal recognition to the fact of Soviet military control of Eastern Europe since the end of World War II in exchange for an opportunity to weave the Soviets into a web of economic, technical and human mutual interests so strong that they could not afford to jeopardize them by acting aggressively.

Under the Carter administration, the perception of West European leaders was clearly that the psychological if not the military balance was tipped in favor of Moscow. So, when the Soviets went into Afghanistan, it was the West Europeans who acted as if they could not afford to jeopardize the web of mutual interests they had built up with the Soviet Bloc. The web metaphor seemed to give way to the double-edged sword image.

The Soviet decision to let the conference go forward clearly showed that Moscow still thinks it has more to gain than to lose by continuing the detente process enshrined in the Helsinki accords. But, if, as the French saying goes, "the manner of giving is worth more than what is given," then the Soviet commitment to detente seems somewhat weak.

In any case, it seems clear that the Soviets were not very interested in paying much to the outgoing Carter team while Reagan is in the wings waiting to be subjected to Soviet probing.