The Carter administration has assured Israel that future military and economic aid will not be linked to the outcome of the Camp David summit on the Middle East, Secretary of State Cyrus R. Vance told the Senate Foreign Relations Committee yesterday, according to informed sources.

Testifying at a closed-door session, Vance said he gave the assurance that aid would not be held hostage against the outcome of the Sept. 5 conference to Prime Minister Manachem Begin last week in Jerusalem, the sources said.

The Carter administration has repeatedly called on Begin's government to show more flexibility in negotiation with Egyptian President Anwar Sadat.Israeli officials have feared that Washington might try to pressure them with aid reductions or through a "reassessment" similiar to the one undertaken by the Ford administration during negotiations in 1975.

Those fears were evidence by questions directed at Vance yesterday during his report to the committee on his five-day trip to the Middle East last week, which produced agreement by Begin and Sadat to meet with Carter at Camp David.

The United States currently provides about $2 billion a year in total aid to Israel. The assurances from Vance against reprisals evidently helped produce a euphoric reaction by Begin to last week's visit and the invitation to the summit.

Vance left Washington yesterday for an overnight stay in Middleburg, Va., where he will meet with the administration's three top Middle East specialists, Harold Saunders, Albert Atherton and William Quandt, for uninterrupted discussions of plans for the summit. The four men will be staying at a private home in Middleburg.

A senior administration official said that initial planning centered on having President Carter meet separately with Begin and Sadat to open the summit. After these one-on-one sessions, Begin and Sadat would meet alone, and then the three leaders would come together, the official said.

No time has been set on the summit, and estimates of its length by officials range from two to 10 days.

During his testimony yesterday, Vance reportedly refused to be drawn into a detailed discussion of how the United States would carry out its self-described mediator's role at the talks. While keeping U.S. options open on presenting suggestions to both sides, he avoided code words that provoke controversy, such as Sadat's description of the proper American role against of being a "full partner."

Senate sources said Vance's appearance was one of the most forceful yet before the committee. In contrast to a similar briefing he gave just before leaving the Middle East, yesterday's testimony "was much stronger and sharper," one source said.

Vance reportedly emphasized that the summit would focus on expanding the new flexibility that the two leaders have signaled recently in the key areas of continuing security arrangements for Israel and territorial withdrawal by the Israelis from Arab land occupied in the 1967 war.

The security and withdrawal issues are expected to be discussed in the context of the Israeli proposal for a five-year interim administration for the West Bank and Gaza Strip territories, Vance reportedly indicated.

Offering a strong defense of Saudi Arabia. Vance said that Sadat had made the decision to cut off direct talks with Israel on July 30 entirely on his own.

The Egyptian leader told Vance that he had informed the Saudis of his decision after it was taken, and they had supported him in it, but added that they had not pressed him to do it. Vance said the Saudis were supporting Sadat's decision to go to Camp David now.