Egyptian President Anwar Sadat ended his talks here yesterday fortified by support from President Carter on issues at stake in the Egyptian-lsraeli peace talks.

Sadat obtained a reaffirmation from Carter of principles for dealing with the Arab Palestinian problem that lsrael balks at accepting.

This was included in s statement that contained a new warning to lsrael from Carter against establishing additional settlements in war-occupied Arab territory. Carter said any "further settlements activity would be inconsistent with the effort to reach a peace settlement."

ln an emotional farewell between the carter and Sadat families on the South Lawn of the White House, Sadat said that last Friday "l came disheartened and discouraged." Now, he said, "l shall return today back to my country with such perseverence for reaching peace . . . "

That commitment to "perseverance" from Sadat, innocuous as it may seem, was just the most significant evidence of progress during the visit in the judgment of the administration, a senior official said. lt showed, he said, that the peace venture dramatically launched by Sadat's visit to Jerusalem last November is not collasping, despite what Carter described at the farewell ceremony as "temporary disappointments and delays . . . "

No mention was made in the White House statement of any American arms supplies of Egypt, but officials have said it was never intended to announce that while Sadat was here. Egypt is expected to receive F5E jet fighter aircraft, although sadat has also asked for far more advanced supersonic F15s and F16s. More detailed arms talks will follow the sadat visit.

As Sadat left a State Department (See SADAT, A18, Col.1)(SADAT, From A1)luncheon with Secretary of State Cyrus R. Vance, he told reporters he was encouraged by the new, activist role the United States now will take in the Middle East peace talks.

"The United States is not an observer, or a go-between, or a mediator," Sadat said. "No," he said, "the role of the United States now is complete partnership."

Administration officials did not join in that characterization, which would be bound to irritate lsrael. The United States, they insist, is an honest broker, not taking sides.

The White House statement issued yesterday avoided any claim for new American positions or departures in U.S. policy. lt repledged American "historic commitments to the security of lsrael," and declared, as lsrael insists, that a peace settlement "must go beyond the termination of belligerency" and establish "normal peace relations" between lsrael and its Arab neighbors.

At several points, however, there were atatements, described as reaffirmations, that provide new comfort for Egypt and some new discomfort for lsrael, in the judgment of many diplomatic observers.

Carter reiterated, it said, that a peace settlement "must be based on all the principles of Security Council Resolution 242, including withdrawal of lsraeli armed forces from territories occupied in 1967 and the right of every state in the area to live in peace within secure and recognized boundaries."

That is the standard U.S. position. But then the statement also added the sentence: "Resolution 242 is applicable to all fronts of the conflict."

Carter, in the farewell ceremony , underscored the same point, specifying the applicability of "Resolution 242 on all the fronts."

An administration official told reporters at a White House briefing that this phrase was not intended as a criticism of the offer by lsraeli Prime Minister Menachem Begin for resolving the Palestinian problem. Begin has offered "self-rule" for Arab Palestinians in the lsraeli-occupied West Bank of the Jordan River and in the Gaza Strip, in contrast to Sadat's demand for "self-determination" and an ultimate independent Palestinian state.

Nevertheless, other diplomatic specialists agree that by underscoring the withdrawal of lsraeli forces from "all fronts of the conflict," President Carter was emphasizing ultimate lsraeli troop withdrawal from the West Bank and Gaza Strip, and from other regions. Under the Begin plan, lsraeli troops would maintain security in the West Bank-Gaza areas for an undetermined period.

There was another significant diplomatic subtlety in another restement of the U.S. position. The statement said:

"The President (Carter)reaffirmed what he said at his meeting with President Sadat in Aswan Jan. 4: There must be a resolution of the Palestinian problem in all it aspects; it must recognize the legitimate rights of the Palestinian people and enable the Palestinians to participate in the determination of their own future."

Israel's Regin has balked at that language, which is inteded as a compromise for Sadat's demand for Arab Palestinian 'self-determination.'

This issue was an important factor in the breakdown of the Egyptian-Israeli political talks in jerusalem on Jan. 18. In jerusalem yesterday, before his departure for Geneva, Begin was asked if the Aswan formula is acceptable to hime. He replied bluntly: "We have a formula of our own."

The repetition of the Aswan formula yesterday, an administration planner said, "is an indication of the direction in which we think the negotiations should move."

Carter and Sadat have agreed that U.S. Assistant Secretary of State Alfred L. Atherton Jr. will return to the Middle East for shuttle diplomacy between Cairo and Jerusalem in an attempt to gain agreement on this and other unresolved principles for negotiation.

Atherton is scheduled to meet today in New York with Israeli Foreign Minister Moshe Dayan to discuss the Sadat visit, and Dayan will come to Washington next week for further talks.

Israel is certain to be irritated particularly by the criticism in yesterday's White House statement that "israeli settlements in occupied territory are contrary to international law and an obstacle to peace . . ."

The new rebuke to Israel coincided with reports from Israeli Radio yesterday that settlers are preparing to move into one of three new settlements on the occupied West Bank of the Jordan. Sadat charged here on Monday that the Israeli government "is leading the unholy march on the law-breakers."

In bidding goodbye to Sadat and his wife, Jihan, yesterday, Carter said "I am honored to be with the world's foremost peacemaker, President Sadat, and to share with him a partnership in this worthy endeavor."

Both share the same vision of peace, Carter said. Sadat, he said "well understands the deep commitment of the United States to the security of Israel. And he shares the commitment that Israel will be secure."

Sadat, in turn, lauded Carter for removing the discouagement Sadat felt on his arrival, and said he greatly appreciated the sentiments that the American people have shown to him, adding. "I shall never fail you."

In a special touch of pomp and ceremony for the Sadat departure, the U.S. Army's squad of "Silver Trumpets," originated in the Nixon years, peeled out a farewell to Sadat, who departed for London.