The leaders of France and West Germany warned today that a Soviet intervention in Poland would end detente, but Chancellor Helmut Schmidt reportedly declined a French suggestion that Western nations start drawing up a catalogue of reprisals to be taken if Moscow invades Poland.

To maintain East-West stability, Schmidt and President Valery Giscard d'Estaing said after a two-day summit meeting, the Soviet Union, like the West, should avoid seeking unilateral advantage.

Their appeal for moderation and restraint appeared to be directed mainly at Moscow, and a balance of power was emphasized instead of detente. But other points in the communique seemed aimed at members of the Reagan administration who have talked in terms of restoring an overall U.S. strategic preponderence by new nuclear and other military programs.

While pledging whatever defense efforts are needed to maintain an East-West balance, the two men -- using language described as deliberately ambiguous by a diplomat -- deplored any attempt to start a new arms race or achieve military superiority. In private, Schmidt repeated his preferred formula for desirable Western strength -- "second to none" -- a conference source said.

Dangerous trends in the Polish crisis apparently dominated the two leaders' talks, the latest in a series of biannual summits under the 1973 French-German friendship treaty.

In an explicit warning to Moscow, the final communique said: "It is essential that Poland should be able to solve it serious problems on its own in a peaceful manner and without external interference." It repeated a French-German view, stated after the Soviet intervention in Afghanistan, that detente could not survive another shock like that.

But in the two leaders' talks, Schmidt reportedly clung to a less pessimistic prognosis that Giscard about the probability of a Soviet crackdown in Poland.

Moreover, Schmidt, a politician conscious of how much West Germany and his own party stand to lose if exchanges are cut with East Germany, also remains reluctant to start committing his government in advance to post-invasion scenario, conference sources said.

Giscard, in contrast, who has toughened the French line in recent months, expressed concern about Moscow's overall military buildup and specific signals on Poland, the sources said. They added that the French leader suggested that Western governments should make national contigency plans for sanctions if Moscow moves on Poland.

This difference in approach appeared to provide some confirmation for earlier press reports that Bonn and Paris did not see eye-to-eye on the Polish crisis, a matter confirmed by conference sources.

Nevertheless, both were careful to display a solid public front, partly to enhance the European bargaining position in the first contacts with Reagan administration, diplomats said.

In their efforts to define a European political role and to help salvage a workable political climate in an atmosphere of crumbling detente, the two leaders set out what they called essential conditions for stability.

One was the sharing of world responsibility. In practical terms, this means improved transatlantic consultations, diplomats said.

A second condition was a balance of security. The two leaders pledged to meet defense needs, but also called for renewed arms control efforts. The last condition was moderation, especially as it applied to Poland and Afghanistan.