Greek and Turkish leaders agreed yesterday to resume negotiations, broken off two years ago, in an effort to bring peace to the bitterly divided island ofCyprus.

State Department officials called the agreement, reached after two days of intense talks mediated by U.N. Secretary General Kurt Waldheim, the "most significant advance" since the strategic Mediterranean state was partitioned five years ago.

The Carter administration has given high priority to resolving the Cypriot dispute, which has left the southern flank of the North Atlantic Treaty Organization in disarray. The loss of Iran as a strong U.S. ally in the region has given these efforts greater urgency.

In their meeting with Waldheim yesterday in Nicosia, President Spyros Kyprianou, the Greek Cypriot leader, and Rauf Denktash, the Turkish Cypriot leader, agreed to begin a new round of talks in Nicosia June 15.

While Kyprianou and Denktash both cautioned against over-optimism about the resumption of negotiations, a State Department official said that a 10-point joint communique released by the two sides provided a "very solid foundation" for new talks.

From accounts available here of the two days of talks with Waldheim, the U.S. official said, "It appears both parties are determined to make progress."

As evidence of this determination, State Department officials pointed to three provisions in the communique; a commitment to "substained" talks, Turkish willingness to allow Greek Cypriots to return promptly to Varosha, a former Greek Cypriot resort center, and acceptance of the concept of an independent, nonpartitioned Cyprus.

Denktash, president of the Turkish Federated State of Cyprus, a state recognized only by Turkey, said yesterday's agreement was "wonderful, a miracle, much more than 1 had expected."

But he added that "a final solution will not come easily . . . There are still a lot of major differences."

Kyprianou told reporters: "We now have a better understanding of each other's position and point of view. If there is to be a satisfactory settlement, there must be strict adherence to the agreenent reached today."

Cyprus has been divided since July 1974, when Turkish forces invaded the island. Turkey contended that the rights of the Turkish minority there were threatened and that the island was in danger of becoming apart of Greece.

Since then, Turkey has controlled the northern 40 percent of the island although Turkish Cypriots make up only about 18 percent of the population. Nearly 200,000 Greed Cypriots who lived in the area now controlled by Turkey are now living as refugees in the south.

TheUnited States, and especially the Carter administration, has made several efforts to resolve the dispute between the two sides-and their patrons in Athens and Ankara. But as recently as a year ago, Kyprianou bitterly dismissed suggestions of new talks, Saying, "There is no room for bargaining or negotiating.?

Citing strategic defense needs, the Carter administration won Congressional approval last fall for lifting a U.S. arms embargo of Turkey imposed at the time of the 1974 invasion.

Congress, however, required Preisdent Carter to certify, before lifting the embargo, that Turkey was "acting in good faith to achieve a just and peaceful settlement of the Cyprus problem, the early peaceable return of refugees to their homes and properties, continued removal of Turkish military troops from Cyprus and the early serious resumption of intercommunal talks" toward a negotiated settlement.

Yesterdays agreement to resume talks in the first clear evidence of the Turkish attitude envisioned by thepresidential ceritfication, one U.S. observer said.

In addition, thereis also preliminary evidence that the number of turkish troops in Cyprus has been reduced form 30,000 to about 25,000 in recent months.Yesterday's agreement said both sides agreed that "demilitarization of the Republic of Cyprus is envisaged" but it gave no details.

So far no GreeK Cypriot refugess have been allowed to return to the Turkish-controlled sector, but yesterday's agreement gave priority to the resettlement of Varosha, a suburb of Famagusta. Varosha was once a leading Greek Cypriot coastal resort but it is virtually empty now.

A year ago, the Turkish Cypriots expressed willingness to allos the 30,000 Greek Cypriot former residents and businessmen of Varosha to return. But the proposal was partof a package that the Greek Cypriots rejected fot other reasons.

The last talks between the two sides were held in Vienna in 1977, after ClarkClifford, serving as a U.S. presidentail envoy, prepared the way with meetings in Athens and Ankara.

Both sides agreed in Vienna that Cyprus should be a federated republic with Turkish and Greek sectors.

The Turkish Cypriots, however, wanted a weak federal government and wanted to retain most of the territory Turkey had seized in the invasion. The Greek Cypriots wanted a strong and central government, with Turkey returning half of the land it controlled, and these disagreements led to a beeakdown in the talks. CAPTION: Map, the Turkish-controlled area is shaded. By Dave Cook - The Washington Post