TURMOIL IN THE EAST BLOC : Shevardnadze Calls at NATO, Warns Against Reunification : Diplomacy: The Soviet foreign minister says those pushing for one Germany endanger European stability.

As a measure of the new thaw in East-West relations, Soviet Foreign Minister Eduard A. Shevardnadze paid an unprecedented call at NATO headquarters here Tuesday, but he quickly followed the visit with a stiff warning that those pushing for German reunification endanger European stability.

“It is necessary to proceed on the basis of the postwar realities--namely, the existence of two sovereign German states (who are) members of the United Nations,” Shevardnadze told members of the European Parliament’s political committee. “A retreat from that is fraught with destabilization in Europe.”

He indicated that Moscow could only accept a unified Germany if it were demilitarized and neutral.

“We paid the price of 20 million lives for the existing stability,” he said, referring to the number of Soviets who died in World War II. “Furthermore, can the German people themselves forget the national tragedy brought onto them by Hitlerism?”

Shevardnadze’s remarks constituted the strongest, most comprehensive Soviet rejection of German reunification since the recent fast-moving political change in Europe first brought the issue into the realm of possibility.

He made his statement as West German Chancellor Helmut Kohl met for the first time with his East German counterpart, Prime Minister Hans Modrow.

One senior Western diplomat here called the timing of the speech “less than accidental.” Other veteran diplomats said they saw a clear link between Shevardnadze’s remarks on reunification and his visit to the headquarters of the 16-member North Atlantic Treaty Organization.

Soviet concern about growing reunification pressures, fueled both by pro-unity rallies in the streets of Leipzig and Kohl’s recent parliamentary speech on the subject, has caused Moscow to reevaluate the role of the two alliances, a senior Western diplomat said.

Soviet diplomats reportedly have spoken openly to their Western counterparts here in recent weeks about their concern over the dangers of internal instability in East Germany.

“Until four or five weeks ago, Shevardnadze was talking about dissolving the two alliances, but now he talks of them as forces for stability,” this envoy said. “If you capture East Germany in the Warsaw Pact and West Germany in NATO, then it’s a strong guarantee against reunification.”

Observers interpreted Shevardnadze’s visit to NATO as a specific endorsement of the Atlantic Alliance’s future political role as Europe’s East-West divide gradually melts away.

As he ended his NATO visit, Shevardnadze stressed to reporters the continued need for both alliances. “We believe the Warsaw treaty and NATO in this crucial stage of the European process can play an important stabilizing role in Europe,” Shevardnadze said.

In his subsequent speech to the lawmakers, Shevardnadze underscored the fact that “the two (German) states belong to two different--and what is more, opposing--military-political alliances.”

In the course of his address, the Soviet foreign minister struck other themes. He said Moscow’s former East European satellite states are now free to develop any political or economic system they chose.

”. . . We have no intention of giving any directions to them,” he said.

Shevardnadze also said that Soviet-Czechoslovak consultations on the future of about 70,000 Soviet troops in Czechoslovakia will begin “shortly.” But he added that any talks will be “with due regard for the overall European process of disarmament.”

“The Cold War is over,” he declared, “No one seriously disputes that.” But Shevardnadze warned that turbulence and uncertainty accompanied the present political change, and he returned to the central subject of the German danger.

He called for a gradual, balanced approach to the issue of relations between the two Germanys.

“The foundation of the development of the Helsinki process must not be either questioned or destroyed on German soil,” Shevardnadze said, referring to the 1975 Helsinki accords guaranteeing basic human rights that were agreed to by 35 nations.

At a news conference after the speech, Shevardnadze also made it clear his remarks had followed what he called “constant . . . very high-level” Soviet contacts with both the East and West German leadership.

After a working dinner with the 12 European Community foreign ministers here Monday night, Shevardnadze met for nearly an hour with West German Foreign Minister Hans-Dietrich Genscher.

The tenor of Shevardnadze’s remarks were more in the nature of tightly argued concern than the raw verbal bullying that former Soviet Foreign Minister Andrei A. Gromyko so frequently used against the Germans.

Still, the comments provided a sharp reminder of the dangers that remain on the path to greater East-West cooperation. Shevardnadze extolled the prospect of such cooperation during his 90-minute visit to the headquarters of the 16-nation alliance.

He met initially with NATO Secretary General Manfred H. Woerner, then informally with all 16 national representatives, including U.S. Ambassador William H. Taft IV.

The spectacle of a Soviet foreign minister walking the corridors of the alliance headquarters, as employees smiled and applauded politely, left few willing to dispute Shevardnadze’s own description of the visit as extraordinary and unprecedented.

In sharp contrast to his toughly worded remarks about Germany to the European Parliament, Shevardnadze was smiling and buoyant as he approached reporters before leaving NATO. He called the visit “necessary, good and useful” and expressed optimism that important arms control agreements could be attained within the next year.

“We both agree there is a good chance to complete the Vienna talks next year,” he said, referring to negotiations currently under way to reduce conventional forces in Europe.

Shevardnadze said a U.S.-Soviet agreement next year to cut their respective long-range nuclear arsenals by up to 50% was “quite realistic” and that progress on a chemical weapons treaty was “quite encouraging.”

“Let me emphasize that the atmosphere during our discussion was constructive, businesslike and very good,” he said.

Woerner said the Shevardnadze visit “confirmed the changes for the better that we see happening these days, a new openness for a dialogue. The phase of the postwar has terminated, and we are clearly in a new era.”

He added, “(It is) a new era where we are trying to replace confrontation by cooperation and see a chance and an opportunity to get a Europe based on self-determination, democracy and freedom.”

Shevardnadze later said he had been moved by the warmth of his reception by NATO employees. “This was the surprise of the day for me,” he said.