President Carter, in what appeared to be a veiled warning to Israel, raised the prospect yesterday of shifting Middle East peace negotiations to a United Nations forum if U.S. efforts to revive direct Egyptian-Israeli talks fail.

He said the United States would shortly transmit to Israel Egypt's new peace proposals, which he suggested would probably be "a step in the right direction but inadequate."

Should this assessment prove correct, Carter said the United States would attempt to arrange a meeting of Israeli and Egyptian foreign ministers with Secretary of State Cyrus Vance "to search out the compatibility" of the two positions, and "see if we can put forward" compromise proposals.

"If all this should ultimately fail," Cater said, "then, of course, the United Nations has a role to play in the Middle East and has for a long time.

"And as you know, the Geneva conference is, as a result of the United Nations resolution, the basic framework for peace and that is always a fallback position if we fail as an intermediary or mediator," he added.

The president 's remarks, made as Vice President Mondale is visiting Israel, were seen as an effort to impress on Prime Minister Menachem Begin the need to show greater flexibility in responding to Egyptian President Anwar Sadat's peace plan.

The Israelis have always vigorously opposed United Nations involvement in the Middle East peace negotiations. Israel and its friends in the United States also have resisted the reactivation of a Geneva conference because it raised the question of the Palestine Liberation Organization's participation. The Soviet Union co-chairman of the conference, has staunchly supported the PLO.

Carter outlined the prospect for U.S. Middle East diplomacy during a meeting with visiting news executives Friday. The text of his remarks was released yesterday afternoon.

In an unusual move, the White House press office added a footnote to the text of Carter's remarks to explain his reference to the likelihood that Eygpt's peace proposals would be "inadequate."

"By using this term," the footnote said "the president wishes to make it clear that he means that the entire Egyptian proposal is unlikely to be totally acceptable to the Israeli government."

In his remarks to the news executives. Carter said that we have not been able so far to get Begin and Sadat to continue their discussions.

"I believe the next step in the process probably following the vice president's visit, will be the promulgation, or at least the delivery to Israel of the Egyptian peace proposals.

"My guess is it (the Egyptian plan) will be a step in the right direction but inadequate in which case my own inclination would be to try to bring those two nations together at least at the foreign minister level to search out the compatibility and incompatibility of the two proposals.

"Following that, I think my responsibility would be to analyse those differences and compatibilities and see if we can put forward, as we have for years, some compromise proposals which the two governments would then consider.

"If all of this should ultimately fail," Carter concluded, his fallback position was the United Nations and the revival of a Geneva conference.

American officials said that Egypt was expected to come up with its plan shortly but that the administration was already trying to arrange a meeting of the Israeli and Egyptian foreign ministers in London later this month.

Referring to Mondale's visit, Carter told the news executives that the vice president "will be doing some symbolic things to show the Israeli people we genuinely do care about them, we are staunch in our commitment to their security, their freedom.

But Carter once again said he was "disappointed" by the Israeli government's response to U.S. questions about Israeli plans for the occupied West Bank and Gaza Strip.

Israel and Egypt broke off their direct peace negotiations last January primarily because of disagreements concerning the future of the West Bank and Gaza.

U.S. officials have stressed that the Israeli government would ultimately abandon the concept of indefinite military control over the West Bank and limited Palestinian Arab self rule. Such a shift would open the way for possible border adjustments and some form of self-government for the West Bank.