President Carter's special envoy Clark Clifford wound up two days of talks with Greek government officials today, aimed at defining what role Washington can play in resolving the Cyprus crisis and the festering Greek-Turkish imbroglio over airspace and potential oil deposits in the closed Aegean sea.

The talks between the 70-year-old former U.S. defense secretary and the government of Constantine Karamanlis ended with a sense of guarded optimism among Greek officials that a major revision of U.S. policy towards Greece, Turkey and Cyprus was now under way. There was also an appreciation of Clifford's interest in bilateral differences between Athens and Ankara, in an area where Cyprus previously occupied first place.

But officials cautioned that there will be no clear indications of what movement is possible in resolving the stalemated crises until after Clifford's visit to Ankara, the third leg of his fact-finding mission which begins Sunday.

The nearly three-year-old animosity has played havoc with the NATO alliance and brought members Greece and Turkey dangerously close to war.

Clifford relayed the new administration's views on shoring up the NATO alliance, and its concern over Greece's refusal to cooperate with Turkey in NATO matters and nominal withdraw from the alliance's military wing.He reportedly spent most of his time in Athens listening however, trying to draw detailed positions from the Karamanlis government and to establish areas for potential compromise.

Following a briefing by Karamanlis the two men discussed Cyprus, Anti-Americanism, the terms for Greece's return to NATO once the Cyprus and Aegean crises are behind it, and the future of key American military installations in Greece.

The Greeks reportedly gave top priority, however, to their confrontation with Turkey over the Aegean Sea, documenting their own appeals for negotiations and arbitration, which have made little headway in the past two years.

"Clifford was told that the Greek side has shown restraint and moderation," said a source close to the talks, "But that channels of communications are now stalled between Ankara and Athens. Washington's role must be to break that impasse. Otherwise, there are only two courses available: judicial arbitration, which the Turks have rejected, or, if Turkish provocation continues, it would almost certainly lead to war."

On the question of joint oil exploration of the Aegean with Turkey, Karamanlis is reported to have reaffirmed his previous stand: This is an option to consider in the future but only after the continental shelf has been delineated and thus each country's jurisdication defined.

On the question of Cyprus, Clifford met with increased sensitivities and suspicious here. Last week's meeting between President Makarios and Turkish Cypriot leader Rauf Dentkash revealed the hard reality of how far apart the two communities remain on key issues concerning the island's future. The meeting took place after quiet, but intense, American pressure. The Carter administration was reportedly urged to continue the proding, but discretely, through the offices of U.N. Secretary General Kurt Waldheim.

Disgrunteld over what they considered the pro-Turkish policies of the Ford administration, during which Greece's anti-Americanism reached its peak, government sources viewed the Clifford visit as a positive first step in repairing badly damaged bilateral relations with the United States.

"Clifford came on a fact-finding mission," one source close to Karamanlis said, "and now he has the facts. He now knows who's trying to upset the status quo in the Aegean; who's threatening with words or deeds; who's established a new army, with the largest amphibious landing force in the Mediterranean, poised offensively towards the Dodecanese Islands of Greece.

"Whether there will be a change in American policy remains to be seen. But the mere fact that even the possibility of a change (exists) has brought a change in Turkish attitudes . . . this is itself shows how strong a role the Americans can play."