Greek Cypriot President Spyros Kyprianou and Turkish Cypriot leader Rauf Denktash will arrive here Monday for the first high-level negotiations in five years on the reunification of their divided island.

The success of Secretary General Javier Perez de Cuellar in cajoling the two men into "proximity talks" in his 38th-floor U.N. office, diplomats said, has both surprised and pleased officials in foreign offices and defense ministries from Washington to Moscow.

The Cyprus dispute is of long standing and erupts into news headlines because of the NATO membership of Turkey and Greece, the patron nations on whom the Turkish and Greek Cypriots respectively depend.

Every potential crisis in Cyprus raises fears in Washington that the southeastern flank of the alliance will be damaged. Problems there also raise fears in Moscow that NATO will partition and swallow up the strategically located and nominally nonaligned nation.

The dispute has been simmering since 1964, four years after the forced marriage of Greek and Turkish Cypriots, a union imposed by Greece, Turkey and the departing British.

Since that time, a U.N. peacekeeping force has patrolled the island while a succession of secretaries general has put forward a series of compromise plans aimed at reuniting the two communities in a federal state.

Perez de Cuellar, who served as U.N. mediator on Cyprus before becoming secretary general in 1982, has submitted three different negotiating frameworks within the past year.

The first was scuttled in November when Denktash declared "before the world and history the establishment of the Turkish Republic of North Cyprus as an independent state." The second evaporated this spring because, Perez de Cuellar reported, Denktash reneged on the scope of an earlier offer.

The Peruvian diplomat tried again on Aug. 6 in Vienna, presenting to each side what he described as "working points," on which he asked the two leaders to negotiate.

U.N. officials said Perez de Cuellar also was motivated by a growing realization, which is shared by Western diplomats, that the status quo on the island cannot be sustained because pressures are rising in the Turkish community to institutionalize its quasi-independence and because of the military imbalance on the island.

Turkey has kept 25,000 troops on the northern third of Cyprus since its invasion in 1974, more than enough to protect 120,000 ethnic Turks from 500,000 ethnic Greeks.

The plan put forward by the secretary general last month envisions an agreement going into effect by stages in three main areas -- "confidence-building measures," territorial readjustments and the structure of the federal government. In the initial stage, the following would start simultaneously:

*Greek Cypriots would be permitted to resettle refugees from the 1974 Turkish invasion in the east-coast resort town of Varosha and in six other zones. The seven zones would remain under temporary U.N. administration.

*Turkish Cypriots would be allowed to use Nicosia Airport under U.N. administration. This would give them a commercial air route off the island. There is now only a small airport with limited flights to Turkey in their zone.

*A moratorium on actions that could imperil the negotiating process. This would put off a referendum on a constitution for the Turkish state. It would ban attempts by Greek Cypriots to win favorable resolutions in the U.N. General Assembly. And it would cut off attempts by the Turkish Cypriots to win international recognition through the 42-nation Islamic Conference Organization.

*"Technical teams" from each side would try to strike a constitutional balance, and an interim government would be set up with operating foreign and finance ministries.

*A binding agreement would be reached on the eventual powers of the central government, in particular the role of the presidency.

There has long been agreement that legislative power would be divided along the American model -- with equal representation of each state in the upper house and Greek Cypriot control of lower house by a margin of about 7 to 3.

In the Greek Cypriot community, the Communist Party and the rightists have backed the U.N. plan, while elements in Kyprianou's own party have expressed reservations. It is tempting for the Greek Cypriots to hold onto full control of their internationally recognized government, rather than give the Turkish community the extensive veto powers they demand, and be forced to share the benefits of the economic boom their part of the island is experiencing. But some Greek Cypriot officials appear to realize that their community's position can only erode, diplomats said.

The Turkish Cypriots also find it tempting to pursue independence rather than negotiating a return to an island federation. They would prefer dependence on the Turks to dependence on the Greek Cypriots. Only if they are convinced they can have true equality are they likely to bite at the U.N. plan.

The Ankara government, by far the most potent factor, appears divided on the U.N. plan, even though Washington has been pushing it to cooperate.