MOSCOW, MAY 25 -- Soviet President Mikhail Gorbachev said today that the Kremlin may be forced to reconsider its attitude toward disarmament talks and other aspects of the European security process if the West insists on including a reunited Germany in the NATO military alliance.

Gorbachev made no direct threat to withdraw from East-West negotiations, nor did he specify how his country's positions in the talks might change. But his remarks represented the strongest warning yet from the Kremlin that membership in NATO by a united Germany could disrupt East-West relations.

The Soviet leader made his comments at a joint press conference with French President Francois Mitterrand after three hours of talks in the Kremlin that were dominated by the issue of German unification. He also endorsed a proposal by the French leader for creation of pan-European institutions to act as a political bridge between both sides of the continent, without specifying the precise form of such institutions.

A French presidential spokesman, Hubert Vedrine, said earlier that France had detected a stiffening in Soviet attiutudes on German unification and a slowdown in talks in Vienna on conventional arms cuts in Europe. Secretary of State James A. Baker III recently said the Kremlin had failed to respond to new U.S. proposals on troop reductions in Europe.

Western diplomats here say that Soviet leaders appear unwilling to grapple with the strong Western drive to make a future united Germany a member of the North Atlantic Treaty Organization, but the diplomats expect the Soviet Union in the end to be compelled to accept the idea. The issue is an emotional one for the older generation of Soviet politicians, who view the neutralization of the German threat after World War II as an outstanding military and political triumph.

At his press conference today, Gorbachev said that the Soviet Union still has the right to keep its troops in East Germany under agreements signed with the three Western Allies at the end of the war. The Soviet Union "will remain where it is now with its group of troops" if a reunified Germany joins NATO, he said.

Gorbachev and Mitterrand both called for a formal peace treaty to draw a final line under World War II and establish new security arrangements in Europe.

The Soviet leader said that the West would probably react with alarm if there were any suggestion of a unified Germany's joining the Soviet-led Warsaw Pact. He said Western governments should, therefore, understand that it was necessary for the Soviet Union to reconsider its attitude toward "all the negotiating processes" in Europe, including the conventional arms talks and the 35-nation Conference on European Security and Cooperation.

"We must take a look at whether we should pursue the same policy, whether we should base it on the same approaches," Gorbachev said.

Hinting that he might be prepared to envisage German membership in NATO under certain conditions, Gorbachev said that one possibility would be for Germany to follow the example set by France. Under former president Charles de Gaulle, France withdrew from NATO's integrated military command but remained a member of its political structure.

At the press conference, the Soviet president denounced the leaders of the rebel Baltic republic of Lithuania as "a group of adventurists speculating on the noble feelings of the people" and again called on them to rescind their March 11 declaration of independence. He noted sarcastically that the Lithuanian parliament had decided not to "make a gift to President Gorbachev" on the eve of his trip to the United States next week.

Lithuania has agreed to suspend implementation of its independence declaration for the duration of negotiations with the Kremlin, but has refused to rescind the declaration itself. Gorbachev is insisting that the declaration be revoked or, at the very least, frozen before talks can begin.

The economic situation in the republic is deteriorating day by day because of fuel shortages caused by the Soviet economic blockade. Lithuanian officials today said that hot water had been cut off to most factories in the republic and that 100,000 people would be out of work by Monday.

A spokesman for the anti-blockade commission, Alexandrius Ambryazavicius, said he expected that Moscow would supply Lithuania with energy for the duration of Gorbachev's stay in the United States. "As soon as {Gorbachev} comes back, he will no longer have to put on a nice face and then the additional supplies will be stopped."

Foreign journalists have been banned from traveling to Lithuania under restrictions imposed by the Kremlin.