Six months of negotiations on the future of four U.S. bases in Greece collapsed today under the pressure of approaching elections that could bring to power Socialist Andreas Papandreou, a critic of the American presence.

Operation of the bases will continue through the elections under the existing agreement, which has no time limit, and the government of Premier George Rallis indicated that he would insist on a fresh start in the talks if reelected.

Foreign Minister Constantine Mitsotakis said the talks had been "suspended" because there was not enough time to work out a full agreement before the end of the parliamentary session next month. General elections then follow in the fall. The latest poll in the Athens area shows the Socialists leading Rallis' conservative New Democracy Party, which favors retention of the bases, 39 percent to 30.

Rallis had appeared to be making demands for keeping the bases that were unacceptable to the Americans as a means of countering Papandreou. Now the premier is expected to assume a stance of having stood up to the U.S. negotiators, at the same time hoping to diminish the bases issue in the campaign.

The U.S. Embassy expressed "disappointment" over "the Greek government's decision to suspend the negotiations." American officials previously had indicated that they preferred to sign an agreement before the Greeks went to the polls.

The United States maintains four major bases and a number of ancillary facilities in Greece under the terms of a 1953 bilateral defense agreement negotiated after Greece joined NATO. Had an accord been reached, it would have superseded that agreement.

The bases at Nea Makri and Hellenikon near Athens and at Souda Bay and Herakleion on Crete Island serve as staging and supply posts for U.S. and NATO naval and air forces and permit monitoring and surveillance in the eastern Mediterranean. There are 3,400 U.S. personnel and a similar number of dependents.

A new set of defense cooperation principles regarding the bases was initialed by the two countries in 1976 but not ratified by Greece. At that time, Greece had left NATO's military wing to protest the 1974 invasion of Cyprus by fellow alliance member Turkey. The 6th Fleet, which had been based in Greece, returned to Norfolk.

The talks that just collapsed began after Greece's reintegration into NATO last fall.

Papandreou's pledges to "remove" the U.S. bases and pursue a non-aligned foreign policy outside the Atlantic Alliance are addressed to an electorate disillusioned by what was widely regarded as tacit American support for the 19674 military dictatorship, and by NATO inaction over the invasion of Cyprus, which brought Greece and Turkey close to war.

The note of defiance these pledges contain plays to the Greeks' strong pride. It suggests a throwing off of the foreign yoke often alleged to have directed Greece's fortunes since independence in the 1800s.

New Democracy, trying to present a tough bargaining stance in the base talks, reportedly demanded compensatory aid at levels beyond what the United States is willing to grant.

Indications that Rallis' negotiating team may have overplayed its hand came early on in the negotiations, with reports that the American side was unwilling to concede to Greek demands for a fixed 70 percent of the level of military hardward provided NATO neighbor Turkey, a far larger country.

Two other items of discussion, the powers to be accorded the nominal Greek commanders of the bases and the possible use of the base facilities for the planned U.S. Rapid Deployment Force for Persian Gulf action, also reportedly proved to be stumbling blocks.

The French Socialist victory last month gave the Greek Socialists a boost and the weakening of centrist parties here has added to the party's influence.

Observers warn against applying the current poll percentages favoring the Socialists nationwide. Less than a third of the 9.5 million Greeks live in the urban area centered on Athens. While it is widely thought that Papandreou could win a plurality of the vote, it is less likely that he could win a majority or even form a majority coalition with the smaller Communist Party, which also favors ouster of the bases and withdrawal from NATO.

Lately, Papandreous has appeared to moderate his rhetoric on the issue.

The emotional appeal of the Socialist anti-U.S. stance could falter on practical considerations about what would happen once the Americans went home. Many Greeks, uneasy about what they widely believe to be Turkish expansionist designs in the Aegean Sea area, are as concerned about national defense as they are about national pride.

Issues of air- and sea-space control in the region are unresolved. Greece has charged repeated Turkish violations of its seas and airspace in the last three months. The fact that Greece obtains 80 percent of its arms from the United States on subsidized terms weighs heavily on civilians as well as the military.

Papandreou's declared policy of turning away from the West could also collide with Greeks' "European" sensitivity -- fostered by centuries of underdevelopment in which Greece was relegated to the status of a backward annex to Western Europe.

Indeed, some observers now feel that for many Greeks the traditionally high-priority election issue of foreign policy has been superseded by economic considerations. The citizens of this newist member of the European Community are striving aggressively for their slice of the consumer pie.