CAIRO, JULY 16 -- Syrian President Hafez Assad flew home today after a three-day visit to Egypt that marked a formal end to one of the Arab world's deepest rifts and promised renewal of an active political partnership between Israel's two most powerful neighbors.

Officials on both sides said that Assad's trip here, his first in nearly 14 years, was clear and dramatic evidence that the bitter hostility between the two countries brought on by Egypt's signing of a separate peace treaty with Israel in 1979 has been replaced by a new era of cooperation.

How this new cooperation will affect progress toward an overall Middle East peace settlement is not yet clear; even as allies in former years, Egypt and Syria competed aggressively with each other to assert leadership of the Arab world.

But Assad's willingness to visit Egypt, Egyptian officials said, appears to indicate that he is at least considering new approaches in his long effort to regain control of the Golan Heights, which Israel captured from Syria during the 1967 Middle East war and annexed in 1981.

Cairo is clearly hoping that Syria will now actively and openly support its efforts to draw Israel into negotiations on furthering Palestinian self-rule in the Israeli-occupied West Bank and Gaza Strip, thus presenting Jerusalem with a more unified Arab position on the fractious issue.

After losing the Golan Heights in 1967, Assad expanded his military and political ties with the Soviet Union and for many years led the "rejectionist" camp of Arab states -- avoiding negotiations on a final peace treaty with Israel in the belief that such talks would be fruitless until Arabs became as militarily powerful as the Jewish state.

Pursuing this goal of "strategic parity" with Israel, Assad took on what U.S. officials regarded as a spoiler role in U.S.-sponsored Middle East negotiating efforts. Syria's strategic position, its military strength and Assad's adeptness at playing Arab regional politics make it an essential party in any overall Israeli-Arab peace settlement.

But whether on the Israeli-Palestinian issue or the 14-year-old civil war in Lebanon, where Syria has sought to impose its will with a force of 40,000 troops, Assad often adopted inflexible political positions or declined to join peace intiatives.

He has also allowed anti-American terrorists to operate from his country and waged a bitter personal feud with Palestine Liberation Organization Chairman Yasser Arafat, arming and supporting Arafat's political rivals and deepening PLO disunity. The two men are still at odds.

But the end of the Cold War and the Soviet Union's subsequent reduction in military and political support for Syria challenged the foundations of Assad's regional political strategy. Assad adjusted to this new reality by quietly seeking -- and gaining -- improved ties with the United States and by agreeing last December to restore diplomatic relations with Egypt.

Before the rupture of relations in 1979, the last major combined endeavor of Egypt and Syria was their joint attack on Israel on Oct. 6, 1973, which was also Assad's 43rd birthday. Apparently hoping to persuade the Syrian leader, now 59, that a new Syrian-Egyptian partnership should concentrate on diplomacy, not war, Mubarak took Assad today on an aerial sight-seeing tour of the Sinai Desert, which Israel captured from Egypt in 1967 but returned after the 1979 peace treaty.

"{Assad} has to reevaluate his approach," said one Mubarak aide. "I believe we convinced him that this is the spirit of the age, that you have to negotiate with your enemies."

Israeli officials appear to be undecided about what the Egyptian-Syrian reconciliation will mean for them. When the two countries restored diplomatic ties in December, Israel's then-Defense Minister Yitzhak Rabin said "the rapprochement could be dangerous for Israel, but it could also neutralize Syria's destructive acts against the peace process."