Greece's new Socialist government, in its first appearance at high-level NATO proceedings, today declared it is observing a "partial suspension" of alliance commitments and said a "process of disengagement is underway."

The statements, made by Prime Minister Andreas Papandreou to NATO's Defense Planning Committee on the first day of its semiannual meeting here, did not specify just what alliance commitments were being suspended and stopped short of a threat to leave the alliance.

They appeared instead to be part of Greek efforts to win agreement from the allies to renegotiate recent accords governing Greek participation in the North Atlantic Treaty Organization command.

Renegotiation has been a goal of Papandreou's Panhellenic Socialist Movement (Pasok) since before it came to power last October. Papandreou's party was elected after a campaign in which he hinted broadly at a Greek pullout from the NATO command similar to that of France in 1966, and charged that membership under present conditions did not serve Greek national interests.

A high U.S. official expressed hope today that the Greek demands for accommodation eventually can be met. The demands, nevertheless, pushed another unknown into the deliberations of a Western alliance already troubled by increasing antinuclear sentiment in Europe and public opposition to the stationing of new U.S. intermediate-range nuclear missiles on European soil.

Prominent figures within the alliance are known to have argued that any change in Greece's status could have a much broader impact in leading other countries where there is considerable anti-NATO sentiment to seek similar changes.

Although the Greek insistence on new NATO arrangements had been reported previously in Athens, today marked the first time it was laid officially before NATO by Papandreou, who is defense minister as well as prime minister in the new Greek government.

Against this background, U.S., West German and other allied officials appeared to stop short of considering the Greek moves a crisis. One West German official depicted the tactics privately as diplomatic grandstanding.

Papandreou's key demand is for a NATO commitment to protect Greece against what Athens regards as a threat from Turkey. The United States and other NATO allies have resisted this in the past, arguing that NATO is designed to meet a common outside threat -- the Soviet Union -- and cannot afford to get involved in disputes among member nations.

"NATO has a responsibility, as long as Greece is a member of the alliance, to defend its frontiers," Papandreou insisted at a news conference tonight, reiterating what he said he had told defense ministers in the closed committee meeting. "The Greek case is unique. In our case, our frontiers are threatened by an ally to the east -- namely Turkey."

Reading excerpts from his statement to the Defense Planning Committee, Papandreou specifically rejected the agreement reached last year between Greece's previous government and Gen. Bernard Rogers, NATO's European commander, setting up Greek reintegration into the NATO command. Greece had withdrawn from the command in 1974 to protest the Turkish invasion of Cyprus.

"We did not accept the arrangement that is militarily and politically unacceptable . . . ," he said.

In particular, Papandreou cited a quarrel between Greece and Turkey about control of air space over the Agean Sea. Greece controlled the area until 1974. Under the agreement with Rogers, control was to be shared between Greece and Turkey under NATO command terms to be worked out in negotiations that are still underway.

It was not clear whether Papandreou's declaration of a "partial suspension" meant these talks would be discontinued. Other issues under discussion include possible location of a NATO regional headquarters on Greek soil and the relative level of U.S. aid to Greece and Turkey.

Defense Secretary Caspar W. Weinberger announced last Saturday that the United States will be "of as much assistance as we can with both military and economic aid" to Turkey. At the end of a visit to Ankara, he said Turkey and the United States will set up a joint military commission to increase defense cooperation that already includes $400 million in military aid for fiscal 1982.

Despite the backdrop of these measures, Papandreou did not mention the Turkish aid issue specifically in his public remarks. Turkish sources said he mentioned the issue only in general terms at the closed session, which Weinberger also attended.

U.S. sources said the question of U.S. bases in Greece also was avoided in the NATO discussions as well as in a meeting last night between Weinberger and Papandreou in anticipation of today's formal session. The Papandreou government has demanded that agreements covering U.S. bases in Greece also be renegotiated.