In an effort to gain the support of Saudi Arabia and Jordan for the Egyptian-Israeli peace treaty, President Carter's national security adviser, Zbigniew Brzezinski, is to leave today for talks with the leaders of these two moderate Arab states, informed sources said yesterday.

Accompanying Brzezinski, the sources added, will be two other top-ranking Carter administration officials: Deputy Secretary of State Warren M. Christopher and Gen. David C. Jones, chairman of the Joint Chiefs of Staff.

Their mission, decided upon yesterday, was described by the sources as the major prong of an intensive administration campaign to dampen adverse raction to the treaty within the Arab world and keep Egyptian President Anwar Sadat from being isolated from his traditional allies.

The sources said the administration is particularly concerned that Saudi Arabia, whose oil wealth has provided considerable aid to Sadat's financially hard-pressed government, not take actions that could cause trouble for Egypt and harm the treaty's chances for opening the way to a Mideast peace.

Saudi Arabia, whose aid to Egypt totals an estimated $2 billion a year, has refused so far to give any support to the U.S.-backed peace initiative involving Egypt and Israel.

Instead, at a meeting of Arab states in Baghdad late last year, the Saudis pledged to join in an economic boycott of Egypt if Sadat signs the peace treaty with Israel. However, the Saudis have not made clear what steps they are likely to take.

The administration officials will be visiting Saudi Arabia at a time when that kingdom's traditionally close ties with the United States have been undergoing noticeable strain. That has been due to Saudi unhappiness over U.S. involvement in the peace talks, U.S. oil policy and the feeling of Saudi leaders that the United States proved ineffective in trying to save the government of the shah of Iran from overthrow.

Despite these problems, the sources said, the administration feels it must make a maximum effort to convince Crown Prince Fahd, the de facto ruler, and other Saudi leaders that the peace treaty with Israel can help Sadat make Egypt a force for stability in the Middle East.

The sources added that the administration also wants to make a strong try at pleading this argument with Jordan's King Hussein They said that is because Jordan is the other major, pro-Western state in the region, and because its coopertion is important to the next stage of the peace effort -- bringing about autonomy for the Palestinian residents of the West Bank, seized from Jordan by Israel in 1967.

Although Saudi Arabia and Jordan are the major targets of the administration's drive, the sources said the United States also is moving to win backing for the treaty from such other Arab countries as Syria, Algeria, Morocco, the Sudan and the Persian Gulf states. The sources were unable to say, though, whether the Brzezinski group will visit any of these countries.

The administration also moved in another direction yesterday to help bolster Sadaths position and tie him closer to alliance with the United States. Richard N. Copper, under secretary of state for economic affairs, left for Cairo last night to begin discussions with Egyptian officials on U.S. financial assistance for Sadat's internal development programs.

White House officals revealed Wednesday night tht the pledges of military and economic aid made by Carter to Egypt and Israel will total about $5 billion over a three-year period.

As a prelude to the bargaining on the military side of that arrangement, Israeli Defense Minister Ezer Weizman arrived here last night. His Egyptian counterpart, Kamal Hassan Ali, is due in Washington today, and both are expected to begin talks with Pentagon officials on the arms aid sought by their respective governments.

In the meantime, the White House moved to deny reports that the peace treaty might be signed here as early as next week. Presidential press secretary Jody Powell said a number of problems -- among them treaty details that still require working out, Carter's domestic travel commitments and a case of flu suffered by Israeli Prime Minister Menachem Begin -- made it highly unlikely that the signing could take place before the week after next at the earliest.

Powell also said that some of the commitments made by Carter, in addition to pledges of aid, might require legislative action by Congress before they can be implemented.

He did not specify what he meant. But reliable sources said later that powell was referring to a U.S. offer to extend to 15 years a pledge to help Israel make up any shortages it might experience in its oil needs.

A five-year agreement to that effect was made with Israel in 1975. Since then, however, Congress has enacted legislation placing restrictions on the export of oil from the Unitd States, and the sources said some kind of new action by Congress may be necessary to allow extending the agreement beyond the original five years.