Greek and Turkish Cypriots have reportedly agreed to a new negotiating approach in order to minimize the risks of stalemate when Cyprus negotiations resume in Vienna Thursday.

The rival sides appear anxious to maintain the diplomatic momentum imparted by Clark Clifford when he visited the region last month as a special envoy of President Carter.

It is understood here that each side will submit a detailed proposal on the issue it considers of paramount concern - for the Greek Cypriots this is territory and for the Turkish Cypriots it is a new federal constitution. Each side has pledged to respond with serious, constructive consideration of the other's propositions.

This approach has apparently been devised to avoid the deadlocks that arose in previous bargaining rounds when the rival sides offered such divergent proposals that negotiators found no points of convergence to start bridging the gap.

In the new talks, U.N. Secretary General Kurt Waldheim, who chairs the initial sessions, is supposed to provide a negotiating agenda insuring that both key issues get equel, simultaneous coverage.

On substantive issues, the two sides' positions remain far apart. Greek Cypriot President Makarios wants a strong central government, a major pullback by Turkish troops and the return of large numbers of Greek Cypriot refugees to their in Turkish-held areas.

Turkish Cypriot leader Rauf Denktash seeks a weak central authority, defensible Turkish lines and an ethnically separate Turkish Cypriot zone with a permanent link to Turkey.

Reconcilation of these positions is expected to be a lengthy process and diplomats rule out the prospect of any immediate major breakthrough.

The same sources are heartened, however, by signs of a shared determination on the part of both sides to see that the negotiations be sustained this time.

Makarios has been increasingly emphatic in informing Greek Cypriot opinion about some painful concessions to be faced as the price of any settlement.

He has spelled but publicly that he "expects" only one Greek Cypriot refugee in 10 - a maximum of about 15,000 - to return to the Turkish - Cyprio - controlled north of the island.

Makarios is hopeful that another 50,000 Greek Cypriots may regain their homes in territory that the Turkish Cypriot side appears prepared to return to Greek Cypriot control.

Asserting his leadership, Makarious has put down incinient opposition in Greek Cypriot ranks, including leftist leaders such as socialist Vassos Lyssarides.

On the Turkish side, the political climate appears to have hardened, primarily because of strong opposition by hardliners in Turkey to any concessions.

Turkish Cypriot leader Denktash, however, appears to be under instructions from Turkish Premier Suleiman Demirel's government to avoid any steps in Vienna that is likely to scuttle the talks.

The outcome of the Cyprus talks will be a decisive factor in the coming U.S. congressional consideration of military aid to Turkey.

While the Carter administration has been at pains to avoid any public linkage, Clifford reportedly informed Ankara that only a serious Turkish effort to reach a settlement was likely to subdue congressional hostility.