The meeting between the leaders of the Greek and Turkish communities on Cyprus collapsed in disagreement today with no immediate prospect that the talks on reunifying the island after 21 years of civil strife would be resumed.

U.N. Secretary General Javier Perez de Cuellar, who has been mediating between the two sides since September, insisted that the gap between them "has never been so narrow," but he conceded that it may not be possible to avert a total breakdown of the dialogue between Greek Cypriot President Spyros Kyprianou and Turkish Cypriot leader Rauf Denktash.

He said that the two sides are ready to continue their contacts with him and that he would try to revive their summit meeting before the end of February -- "if possible."

When the talks began here Thursday, his aides said, the hope was that agreement would be reached on territorial concessions and a new constitution that would establish a two-zone "Federal Republic of Cyprus," with veto powers to protect the rights of the ethnic Turkish minority and a deadlock-breaking mechanism to ensure that the government would be able to function.

But U.N. officials said the tone of the meeting turned sour at the outset when Kyprianou presented a position paper that broadly challenged what Perez de Cuellar had assumed was common ground already established between the two sides through his mediation last fall.

Only late this afternoon, the officials said, did Kyprianou offer to accept the agreement and limit negotiations to four unresolved issues: a timetable for the withdrawal of the 24,000 Turkish troops who have occupied the northern sector of Cyprus since 1974, the location of the areas now occupied by Turkish troops that would be returned to ethnic Greeks, external guarantees that the agreement would be observed and the principle that all Cypriots would be free to own property, settle in and move through any part of the country.

By then it was too late. Denktash rejected the offer, with the knowledge that he could no longer be blamed for the breakdown of the summit, the officials explained.

The failure of the talks was disappointing to the United States and other western governments, which had exerted quiet pressure on both sides and their patrons, Greece and Turkey, to come to terms. An agreement on Cyprus would have eased congressional opposition to an increased flow of U.S. arms to Turkey and would have ended the threat to NATO's southeastern flank that a new Cyprus crisis would pose.

Anticipating that Cyprus would be removed as an irritant in relations with Washington, Turkey's prime minister tentatively had scheduled a visit to the United States in April -- the first since before the 1974 invasion of Cyprus.

U.N. and western officials said afterward that one motive for Kyprianou's stand was that the Athens government had discouraged an agreement on Cyprus. Denktash said today that "Greece doesn't need a settlement because they use Cyprus to punish Turkey in the U.S. Congress with the help of the Greek lobby here in the U.S."

Denktash told reporters after the summit that he doubted that it would be possible to resume negotiations before the end of February. He also suggested that the concessions made in the earlier talks might be withdrawn as a basis for any future summit meeting.

But he offered to meet with Kyprianou in Cyprus, without conditions, to try to find a new basis for an agreement. The concessions he made last fall "do not exist today," Denktash concluded.

Kyprianou maintained his willingness to cooperate fully with the secretary general and attend a new summit meeting that would start negotiations on the basis of the concessions already made. "We don't regard the effort of the secretary general as having ended."

Earlier, a spokesman for Kyprianou, Andreas Christophides, charged that Denktash "wants us to sign a ghost paper, a ghost agreement that does not really exist. We hope the way will still be found out of this impasse not created by us."

Privately, Greek Cypriot officials suggested that Kyprianou had been obliged to raise the issues that he did to satisfy his domestic constituency. They said that public statements made by Denktash and Turkish officials in Ankara had forced Kyprianou to focus on the question of withdrawal of Turkish troops.

U.N. officials initially had hoped that the withdrawal question and the related issue of outside guarantees would be dealt with by working groups after the summit but before a transitional government was established. These issues are among the most ticklish because the two sides are in strong disagreement over whether a token contingent of Turkish troops should remain on the island and whether Turkey should be a guarantor of any ultimate agreement.

Greek Cypriot officials suggested that Perez de Cuellar was responsible in part for the misunderstanding between the two sides because the terms of the agreement he had drafted were insufficiently precise.

But western diplomats who have monitored the negotiations during the weekend supported the U.N. view that Kyprianou had made a tactical mistake in stating his demands too broadly, resulting in the general perception that his side was at fault for the summit failure.