The foreign ministers of 15 NATO countries expressed the desire today "to cooperate in rebuilding international trust" with the new Soviet leadership if Moscow is ready to act "in this spirit."

The statement came in a communique issued following a two-day conference of the North Atlantic Treaty Organization ministers here, who for the first time expressed concern over evidence of communist use of chemical weapons.

The communique specifically called attention to "grave concerns about strong evidence of continued use of chemical weapons in Southeast Asia and Afghanistan in violation of international law, including Soviet involvement in the use of such weapons."

Nevertheless, the tone of this communique, in comparison to one issued in June at the last NATO summit in Bonn, seemed far more positive toward extending an invitation to the Soviet leadership to respond in kind.

For example, the communique "emphasized resolve to develop substantial and balanced East-West relations aimed at genuine detente." While the allies will maintain "a firm, realistic and constructive attitude toward the Soviet Union . . . they desire to improve relations with the member states of the Warsaw Pact and to extend areas of cooperation to their mutual benefit," it said.

Secretary of State George P. Shultz told a press conference that the closed-door discussions about relations with the Soviet Union following the election of Yuri V. Andropov as Communist Party general secretary were "realistic and thoughtful."

"We all are interested to see the development of a more constructive relationship based on a different pattern of Soviet behavior," he said.

Canadian Foreign Minister Allan J. MacEachen said later that the NATO communique was meant "as a signal to Moscow that we are united" in terms of strength but also are ready to respond to "positive gestures."

The communique was sharply critical of continued Soviet military occupation of Afghanistan and of violations of human rights in Poland.

It called on Moscow to show "tangible evidence" that it is ready to respect the independence of other states but said "the allies are open to all opportunities for dialogue, will welcome any positive move to reduce tensions, and desire, if Soviet attitudes allow, to cooperate in rebuilding international trust."

In the crucial area of trade with Eastern Europe, a bread-and-butter issue for many West Europeans aside from the question of helping strengthen the Soviet economy, the new communique is also somewhat less severe than the June communique. In that earlier statement, the alliance talked of approaching East-West economic relations "in a prudent and diversified manner consistent with our political and security interests."

Today's communique first acknowledged the tough times in the West, stating "economic recovery in the West is essential both for allied defense efforts and for social stability and progress."

It then added that "the allies recognize that mutually advantageous trade with the East on commercially sound terms contributes to constructive East-West relations. At the same time, they agree that bilateral economic and trade relations with the Soviet Union and Eastern Europe must also be consistent with their broad security concerns which include the avoidance of contributing to Soviet military strength."

The alliance, under U.S. prodding, is also trying to get five new studies under way that would develop a common Western approach to economic and trade relations with the Soviets.

The meeting today was the first attended by a Spanish foreign minister since Spain joined NATO earlier this year under a previous government. The new Socialist government, however, is reviewing its membership, and NATO Secretary General Joseph Luns said that Spanish representative Fernando Moran listened to the proceedings but did not participate in the dialogue or endorse the communique.