Arab leaders seem prepared for a long diplomatic siege following Secretary of State Cyrus Vance's recent unsuccessful effort to develop momentum for a possible resumption of the Geneva conference.

While they appear to be an appreciation of U.S. intentions to bring about a peace settlement, Israel's firms refusal to give ground on any of the points the Arabs consider essential seems to have dispelled Arab hopes that the Jewish state would quickly jump to Washington's bidding.

"There is not going to be any breakthrough any time soon: we know that," an authoritative Jordanian source said. "We see a time in the future when the little international support Israel still has will begin to break, but in the meantime we will wait and see what the Americans come up with."

Optimistic assessments of the Vance tour from Jordan's King Hussein and Egyptian President Anwar Sadat indicate that the Arabs are content for the moment to continue on the course they have followed for months - working with the United States, and sending out what they consider to be signals of moderation, in an effort to bring Israel into an acceptable negotiating position.

The leaders of Jordan, Syria Egypt, Saudi Arabia and the Palestine Liberation Organization are expected to meet late this month to coordinate their strategy, but diplomatic observers and Arab sources here say no major change in the situation is likely over the next month or two.

The Moslem holy month of Ramadan, which brings the Arab world to a near halt, begins next week, and the indications are that the next Arab move will be to send their foreign ministers to meet with Vance during the U.N. General Assembly session in September.

The Cairo newspaper Al Abram published a statement today by Sadat saying the Arabs are "not in a hurry." Coming from the Arab leader who has in fact been most in a hurry, this seems to show a more realistic assessment of the difficulties ahead.

There seems to be little hope that a Geneva conference on the Middle East can be convened this year. In fact, except perhaps in Cairo, the Arabs had little hope of that even before the Vance trip. The Arabs have been encouraged, however, by indications that the United States is trying to exclude it, and by what they see as an American willingness to discuss substantive rather than procedural matters in advance of a formal conference.

Therefore, according to Arab sources here, it is too soon from the Arab view, to turn their backs on the American diplomatic effort or to drop their conciliatory posture.

Egyptian newspapers today quoted an "official source," which means the Foreign Ministry, as saying that the Vance mission showed that Egyptian-U.S. relations were "going from good to better."

On paper, the Arab and Israeli positions appear to be so far apart as to be irreconcilable, despite Vance's assertions that there is actually agreement on some points.

Informed analysts here and in other Arab capitals agree that this gap is so wide as to assure that at the very least there is a long, difficult diplomatic road ahead before any mutually agreeable settlement can be reached. The self-generated Euphoria that existed earlier this year, especially in Egypt, in which the Arabs convinced themselves that Israel would accept a simple territory-for-peace trade brokered by the Americans, has dissipated.

In a speech yesterday marking the 23th anniversary of his reign, Hussein called for new Arab efforts to "convince the world around us of the justice of our cause."

In the view of analysis here, this fits in with a growing recognition among the major Arab states, with the possible exception of Syria, that they are going to have to do more than wait for the Americans to deliver the Israelis if they really want to get their territory back and achieve peace.

Look, we expect the Americans are now going to squeeze the Israelis and squeeze them some more. Carter cannot go back now that he has come this far. But when the Israeli finally yell uncle, the Americans have to have something from our side to offer them," a Palestinian source commented.

In other words, the Arabs may have to offer things that they have so far withheld - such as a promise of open borders as part of a peace agreement, or a decision by the PLO to accept U.N. resolution that imply the legality of Israel's existence - if they are going to break down Israel's determination.

The first place to look for signs of chance, observers here say, is a meeting schedules for later this month of the PLO's Central Council in Damascus.

If the PLO is going to change its position on past U.N. resolutions in an effort to make itself more palatable to the Israelis, that could be the place where the evidence emerges.