President Carter warned Israel yesterday that refusal to withdraw from the occupied West Bank would be "a very serious blow to the prospects for peace."

Amid new indications of an impending clash between the two nations, Carter spoke in strong terms to a televised news conference against a unilateral Israeli change in the internationally accepted framework for a settlement of the Arab-Israeli dispute.

Prime Minister Menachem Begin and members of his government have told the United States repeatedly in recent weeks that they do not feel bound to withdraw from the West Bank in return for peace under the terms of United Nations Security Council Resolution 242. Carter noted yesterday that such a stand is "a complete reversal of the policy of the Israeli government [in the past] and other governments in the area."

The president disclaimed any intention of applying pressure to Begin in their meetings scheduled at the White House next week, but his press conference remarks themselves were a form of public persuasion certain to add to the roaring political controversy in Israel over peace policy.

Israeli Defense Minister Ezer Weizman, an important political figure who is generally considered Begin's potential heir within the ruling Liknd Party, urged the United States yesterday to put its diplomatic music behind a bilateral Egypt-Israeli deal rather than continue to seek a comprehensive settlement involving the West Bank, Jordan and the Palestinian question.

"I think there is a chance" for a separate arrangement with Egypt, Weizman told Washington Post editors. Later in the day, however, Carter went out of his way twice during his press conference to emphasize that the United States is committed to a comprehensive Middle East agreement.

Weizman, who is to take part along with Begin and Foreign Minister Moshe Dayan in the White House talks, said that in a case of a major and unresolved disagreement next week "there will be black coluds all over Washington."

In such a case, "I would recommend sending an Israeli team to Cairo to see what we can produce out of the wreckage . . . I would do my best to get [Egyptian President Anwar Sadat] to agree to go bilateral," said Weizman, adding that such an indea might be "highly impractical and imaginative."

Another possibility in case of failure in Washington next week is that Sadat would "close shop" on his peace initiative. Weizman said his appears to be somewhat more likely than movement in a bilateral track.

Sadat has insisted from the beginning of his concerted peace bid last November that he will not conclude a pact with Israel for return of the Sinai without fundamental agreement, at least in principle, on Israeli withdrawal from the occupied West Bank and Gaza Strip and a form of statehood and self-determination for the Palestinians. American officials have said they see little or no chance that Sadat will abandon this stand.

Weizman argued that Begin has taken "a phenomenal step" by proposing "self-rule" for Palestinians on the West Bank. Saying that "somehow little Israel is now overpressured," Weizman said he is concerned that Begin will stiffen his stand on Palestinian questions next week if he is placed under U.S. pressure.

Weizman met at lunch and at a later conference with Secretary of State Cyrus R. Vance, and saw members of the Senate and House Armed Services committees on Capitol Hill. Today he is scheduled to meet with Carter.

In his news conference, Carter said that "the prospects for comprehensive peace in the Middle East are quite good" compared to a year ago, but he conceded that the diplomatic situation has "deteriorated to some degree" since Sadat's epochal trip to Jerusalem.

Carter said one of his aims next week will be to repeat to Begin, "perhaps a little more effectively" than U.S. envoys, the requests and negotiating positions of Sadat as expressed in the Egyptian leader's trip here a month ago.

Carter listed remaining Egyptian-Israel differences about the Sinai, which he called "relatively easy to resolve," as the Jewish settlements there, placement of Egyptian forces in the area, continuation of Israel control over some airfields, and the schedule of Israeli withdrawal.

He described the Palestinian question and the implementation of U.S. Resolution 242 - that is, Israeli withdrawal from the West Bank - "more major strategic kinds of differences."

"We have got a long way to go," said Carter of the Middle East diplomatic problem. He added, "I am not discouraged about it. We are going to stock with it. And even if it takes a lot of time and much abuse and much debate and many differences expressed by all public, officials, I intend to stay with it . . ."