Secretary of State Cyrus Vance opened a new phase of post-Camp David diplomacy yesterday with a lengthy effort to convince Jordan's King Hussein to join the U.S.-sponsored peace arrangements.

Hussein, whose government expressed major reservations about the accords Tuesday, was described as serious, deliberate and full of questions during a two and one-quarter hour meeting with Vance at the royal palace. In the end, as anticipated, he was noncommittal.

Vance's efforts to win greater Arab support, in what he termed a "crucial phase" of the Middle East peace drive, were made more difficult by the growing lineup of moderate Arab states that have registered objections to the Camp David agreements.

Another complication was the unresolved dispute over Israeli commitments at Camp David to forego additional Jewish settlements in the occupied West Bank, a subject Vance discussed here with Hussein.

During the day the Persian Gulf states of Kuwait, Qatar and Bahrain as well as Lebanon and North Yemen, all of which are considered moderate Arab nations, issued objections to the Egyptian-Israeli agreements at Camp David. To a large degree these Arab states were believed to be following the lead of Saudi Arabia, whose sharp condemnation of the Camp David accord jolted U.S. officials Tuesday.

Militant Arab states such as Syria, Libya and Algeria which began meeting last night in Damascus, only about [WORD ILLEGIBLE] miles north of here, had been considered automatically in the anti-Camp David ranks. Their opposition was thus of less concern than that of the moderate Arab nations, a grouping in which Jordan has been a prominent member.

Although he had just completed 13 days of hard bargaining at Camp David, which produced the Egyptian-Israeli accords, Vance appeared to be far more confident and ebullient than usual at the start of his sixth major trip to the Middle East in 20 months.

For the first time, he is carrying a detailed and negotiated plan to deal with major aspects of the seemingly intractable Arab-Israeli dispute. He is telling Hussein and other leaders that a historic process is beginning, as a result of Camp David, which bears prospect of settling age-old scores and bringing peace to the region.

The underlying theme of his argument to Hussein is that fundamental change in West Bank arrangements will soon be under way, with or without the participation of Jordan. Vance's view as expressed to reporters aboard his plane by a "senior American official" is that it would be a great mistake" for Hussein and other Arab leaders to pass up the chance to break the Arab-Israeli deadlock.

It is far from a simple matter for Hussein, a buffer state ruler who is affected by many opposing influences. The Jordanian monarch's first reaction, in a statement issued Tuesday, was to criticize aspects of the Egyptian-Israeli arrangements without explicity closing the door to future co-operation.

After the meeting yesterday, State Department spokesman Hodding Carter said, "It is clear that the king and his government are going into this matter with very serious consideration."

Close to half of the two million Jordanians living on the east side of the Jordan River are of Palestinian origin. Jordan, as ruler of the West Bank territory from 1948 until its loss in the 1967 war, also has special responsibility for the 800,000 Palestinians still under Israeli occupation in that area. Jordan still continues to pay the salaries of school teachers, postmen and other municipal officials on the West Bank and aid to the West Bank from which Gulf states is channeled through Jordanian accounts.

For these and other reasons, Hussein has major connections, influence and interests in the West Bank. At the same time the passions which can be unleashed by Palestinian nationalism in the area pose serious dangers to the Jordanian throne.

As illustrated by the prominent role of Jordan in the Camp David plans, the problems of the West Bank can hardly even be addressed without consideration of this country. Regardless of American, Egyptian and Israeli resolve, there is much skepticism here that a serious process toward a political solution for the West Bank can be set in motion, much less sustained, without Jordan's participation.

From the outside Hussein is torn between his militant neighbor, Syria, with which he has increasingly close ties: orthodox Saudi Arabia, which provides about one-quarter of his budgetary support; and the United States, which provides major aid programs, arms and a superpower connection.

Despite talk that the United States will lean on Hussein to back the Camp David accords, it is far from clear that pressure would be effective. Hussein's standing in the Arab world and even his survival could be at stake. And in some respects, given its strategic geography and the availability of other support, Jordan might be able to do without the United States more easily than the United States could do without its links to Jordan.

Hussein's long standing reluctance to become involved in ambiguous negotiations about the future of the West Bank has not changed, from the evidence of his public statement Tuesday and his cautious questions to Vance yesterday. Hussein's basic objection to Camp David's that no commitment was given by Israel to withdraw fully from the West Bank.

There is no expectation that Hussein will make up his mind about participation in the Camp David arrangements before the Israeli Knesset vote on the deal over Sinai settlements with Sadat in about two weeks. Even then, considering the difficult spot he is in, Hussein may be in no hurry to announce clearcut decisions that are certian to displease one or another of the several powers and connections which steady his throne.