Secretary of State Cyrus Vance ended 10 days of intensive talks in the Middle East today without achieving any major progress toward a comprehensive peace agreement.

While Vance refused to concede officially that his mission has failed, a senior Israeli adviser reported that only "a very narrow chance" remains for convening a Geneva conference this year.

In a news conference, Vance said his meetings here with Israeli Prime Minister Menahem Begin have not narrowed the "fundamental differences" and "wide gaps" between Israel and the Arabs on key issues.

Vance said "some" of the Arab states had shown mote flexibility than in the past regarding future relations with Israel, but he did not suggest that this change was important enough to be a major breakthrough.

Shmuel Katz, information adviser and longtime confident to Begin, reported no change in the Begin government's strong opposition to territorial concessions on the West Bank of the Jordan River or in its determinded stand against any sort of Palestinian homeland or entity in territory now held by Israel.These are key elements, in the view of the United States as well as the Arab states, in a comprehensive Middle East settlement.

Katz reported, on the basis of closed-door discussions with Vance, that Arab governments insisted on participation of the Palestine Liberation Organization in a Geneva conference. Israel remains unalterably opposed to this in any form.

"If the Arab countries continue to insist on PLO representation, there will not be a Geneva conference," Katz declared.

Vance is scheduled to touch base Thursday with King Hussein of Jordan, Syrian President Hafez Assad and Egyptian President Anwar Sadat in brief stopovers in their respective capitals en route to meetings in London with British and southern African leaders.

But with no progress to report in the Begin talks, there was little likelihood that Vance's whirlwind visits would yield forward movement in the Arab position.

About the best that Vance can hope for is confirmation that Arab foreign ministers will continue the dialogue in meetings with Vance during the opening days of the United Nations General Assembly session next month.

Israeli Foreign Minister Moshe Dayan will also be on hand. While Vance will meet with all sides, no direct Arab-Israeli meetings are expected and there is no optimism that major progress will result.

Vance told reporters today that he might also meet with PLO representatives, if the organization approves U.N. Security Resolution 242 in its entirety. There are no indications at this time that the PLO would do that.

The failure to achieve any sign of a Middle East breakthrough despite the extensive personal involvement of President Carter, two trips to the area by Vance and more than six months of effort, is another serious foreign-policy setback for the Carter administration.

The United States has stated and the officials involved continue to insist that progress "toward a negotiated peace in the Middle East is essential this year if future disaster is to be avoided."

Vance heard from Arab leaders during his current journey, most notably from the leaders of Saudi Arabia, that the failure to move toward peace would begin the drift toward regional, instability and a fifth Middle East war.

As in his talks with Carter in Washington last month, Begin reported today that there had been "no confrontation" in his meetings with Vance despite the major differences in points of view on key elements of a comprehensive settlement.

A seemingly elated Begin told Israeli reporters in Hebrew outside his office that although five hours of his office that although five hours of discussion with Vance covered both the substance and procedure of an Arab-Israeli diplomatic settlement, the Secretary of State "id not ask anything from Israel. Maybe (the United States) will ask eventually but not until now. Begin and other Israeli officals suggested that, as in the Washington talks, the two sides "agreed to disagree.

Vance informed Israelis again today, in his press conference televised here in full, that "It is not our purpose to impose terms on the parties but to assist them in reaching agreement among themselves."

At the heart of the conflict of views is the U.S. belief, not shared by Begain or many other Israelis, that the Arab countries are sincere in wanting peace. Leaders of the Begin government believe that the Arab governments as well as the Palestinian movement are bent on the destruction of Israeli and seeking return of a West Bank and creation of a homeland only as a step toward waging more effective war against the Jewish state.

Vance said he believes that Begin was "very interested in the conclusion which I expressed to him that the Arabs really do want to make peace." Asked if he had made progress in persuading Begin about Arab good will, Vance replied, "I hope so."

The Secretary, backed by U.S. and Israeli flags in the main dining room of the King David Hotil, was asked if U.S. taxpayers and Congress would be willing to continue massive foreign asistance in military supplies both to Israel and to its Arab neigbors as the region drifts toward war as a resuit of diplomatic deadlock.

Vance replied, "Our commitment to the security of Israel is clear and unequivocal and we will continue to provide to Israel what is necessary to preserve it."

[The Russians, who have long been concerned about having a major role in the Middle East, reportedly gave assurances to the PLO that Moscow Geneva conference in the absence of the PLO, Reuter quoted PLO officials in Beirut as saying today.]