President Carter told a joint session of Congress last night that he is dispatching Secretary of State Cyrus R.Vance to the Middle East today to win support for the Camp David summit agreements from Jordan and Saudi Arabia, two states critical to any peace settlement.

With Egyptian President Anwar Sadat and Israeli Prime Minister Menachem Begin looking on from the congressional gallery, the president told the Congress and a national television audience that "the summit exceeded our expectations, but we know that it left many difficult issues still to be resolved."

It was an emotional scene as Carter received a long, standing ovation when he entered the House chamber. In the gallery, Begin and Sadat stood on the either side of Rosalynn Carter, and when they were introduced by the president each received a loud and sustained ovation from the packed chamber audience.

Announcing the beginning of an American diplomatic offensive to broaden the Egyptian-Israeli accords to include other Arab nations, Carter said:

"We need to consult closely with the Arab leaders, and I am pleased to say that King Hussein of Jordan and King Khalid of Saudi Arabia have now agreed to receive Secretary Vance, who will be leaving tomorrow [Tuesday] to explain to them the terms of the Camp David agreement and to secure their support for the realization of the new hopes and dreams of the people of the Middle East."

No Middle East peace settlement is considered possible without the present of Jordan, which ruled the Israeli-occupied West Bank territory until 1967. The Saudis, Jordan's main financial supporters, are also considered vital to any settlement.

The president's appearance before Congress capped a euphoric day at the White House that was marred only by the angry reaction of some Arab leaders to the agreements and the resignation of Egypt's foreign minister to protest what Sadat accepted at Camp David.

But the official silence from Jordan and Saudi Arabia and their willingness to hear out Vance before taking a position were considered hopeful signs by administration officials.

There were these developments during the day:

Carter telephoned Hussein, whose cooperation is vital to the implementation of the accord covering the West Bank, and reportedly obtained his committment to make no final decision before receiving a full report from Vance. According to U.S. officials, the Jordanian leader made no other committments.

Carter sent a written appeal for support to King Khalid of Saudi Arabia, whose country is also of great importance to the future of the Camp David pacts. The quickly arranged Vance trip to Saudi Arabia is a reflection of the Saudis' critical influence. Carter also sent letters to other world leaders, including Soviet President Leonid Brezhnev, who has strongly opposed Egyptian-Israeli deals.

Begin, who spent the day at his hotel before joining Carter and Sadat at the Capitol, told broadcast interviewers that Israel will refuse under any circumstances to change its position that Jerusalem is its "eternal capital" and that the Egyptian differences with this view are "their problem." Begin also declared, in an interview with ABC's Barbara Walters, that both Egypt and the United States have agreed to an Israeli military presence in the West Bank following the planned five-year "transitional period" there. No such provision appears in the published text of the accords.

Sadat, who spent the day at the residence of his ambassador here, told CBS' Walter Cronkite in a broadcast interview that the participation of Jordan's Hussein is "essential" to the peace process. Sadat said Hussein had sent him a message last week that "I am ready" to resume Jordanian responsibilities in the West Bank, but the Egyptian added he did not know for sure what Hussein will do. Sadat denied that he is signing "a separate peace" with Israel and maintained that solving the West Bank-Gaza problem is "a committment of honor for Egypt."

U.S. officials confirmed that Carter has agreed, subject to Congressional approval, to construct two air-bases in Israel's Negev desert to replace the Sinai airfields which Israel has agreed to relinquish. The U.S. built airfields in Israel may cost about $500 million each, officials estimated.

This flurry of activity was accompanied by a crescendo of praise for Carter and a calculation by White House officials and outside political professionals that the success at Camp David would bolster his shaky political standing.

In Israel, a diverse coalition of political leaders rallied behind Begin, apparently assuring that the Israeli Knesset will agree to Sadat's demand that Israeli settlements be withdrawn from the Sinai desert before completion of a peace treaty between Egypt and Israel.

That first hurdle in continuation of the peace process is set for a Knesset vote in two weeks, but in a far more difficult task involves the attitudes of Hussein and Saudis.

Hussein cut short a vacation in Spain to return last night to Amman, where he has scheduled an extraordinary cabinet meeting for today.There were reports yesterday of considerable skepticism among Jordanian officials about the committments Israel made in the agreements.

Moreover, while there was no official Saudi reaction, the Arab News, an English-language daily in Jeddah that rarely strays from official Saudi thinking, charged in an editorial that the Israeli concessions did not go far enough.

But administration officials expressed satisfaction that both Hussein and the Saudis were withholding their reaction until they have studied the agreements, a course Carter urged on Hussein in his 10-minute telephone conversation with the Jordanian leader.

U.S. officials consider Hussein's participation as a key to the success of future negotiations and the Saudi attitude as a key to Hussein's ultimate decision.

"If the Saudis advise against it, he probably won't go for it," one official said.

After talking to Hussein, Carter yesterday morning briefed about 30 members of Congress, including the leadership and key members of the Senate Foreign Relations Committee and House International Relations Committee, in the White House East Room, the scene of his triumphant return from Camp David Sunday night.

Sources said the president assured the group he made no secret agreements or arrangements at the summit.

According to participants at the meeting, Carter gloomily forecast that the Soviets will react negatively to the agreements. He also heaped praise on Sadat and Begin, singling out the Egyptian president for showing "great courage and flexibility" during the Camp David talks, the sources said.

Meanwhile, some of the details of the extraordinary 13 days at the presidential retreat began to seep out from a variety of sources.

The president, for example, told the congressional group that the summit could have collapsed at a number of points. Confirming the impressions of observers, he said he deliberately kept Sadat and Begin apart for most of the summit because their initial meeting was so acrimonious and heated that no process seemed possible, sources said.

Sadat and Begin met together on Sept.6 and 7,but never formally met together again as Carter worked out the details of the agreements with them separately.

After Sadat, according to his own testimony in a television interview yesterday, threatened to walk out of the summit late last week, the key breakthrough occurred during a 4 1/2 hour meeting Friday night between Carter and Begin. It was at this meeting, sources said, that Begin agreed to the provisions governing the Palestinian role during a five-year transitional period for the West Bank of the Jordan River and to the agreement to have the Knesset decide the future of the Israeli settlements in the Sinai within two weeks.

The final snag at the summit involved Jerusalem, an issue that was left unsettled as the three governments agreed to exchange letters stating their positions. The letters are to be made public today.

President Carter's reception on Capitol Hill last night underscored vividly the impression that the gamble he took in convening the Camp David summit would pay handsome political dividends at least in the short run.

"It clearly shows the president's skill at handling very tough international problems and it should put an end to all of the talk about competence and whether he's up to the job," one White House official said.

Other assessments were less enthusiastic but there was general agreement that Carter's troubled presidency had received an unexpected and impressive boost from the outcome of the Camp David talks.