Israeli leaders underscored yesterday that a resumption of direct negotiations with Egypt cannot be taken for granted if President Anwar Sadat's new peace proposals contain preconditions demanding an Israeli pullout from occupied territories.

Foreign Minister Moshe Dayan, moreover, indicated yet another qualification when he said that the full Israeli Cabinet would have to consider whether Israel should send Dayan to London this month to meet with Egyptian Foreign Minister Ibrahim Kamel and Secretary of State Cyrus Vance.

A Foreign Ministry spokesman, who said Israel has not yet received Sadat's proposal, noted that "if this is a bona fide peace plan like Israel has submitted and there are no preconditions and Israel doesn't have to sign anything before going to London, then Dayan will go."

Similar caution was expressed by Prime Minister Menachem Begin. Speaking in a radio interview, he said, "In principle we would like to see the foreign ministers meet. But we will have to read what's in the plan and then we will make the decision."

Israeli officials said they expected to receive Sadat's plan today from U.S. Ambassador Samuel Lewis after the Egyptian leader makes it public at his Mediterranean rest home near Alexandria, Egypt.

On Monday, Sadat said he had given Vice President Mondale the details of the new Egyptian peace proposal to convey to Washington and Jerusalem. Sadat also formally accepted an American invitation to send his foreign minister to the London conference. The meeting was tentatively scheduled for the week of July 17.

The substance of the Egyptian proposal was not known here but there were press reports that it may include the suggestion that the occupied West Bank and Gaza Strip be returned to Jordan and Egypt respectively on an interim basis pending a negotiated settlement of the ultimate status of the areas.

According to these reports, the Egyptians also are proposing dismantling of Israeli settlements under U.N. supervision over a period of five years. Details dealing with the question of sovereignty, Palestinian rights and Israeli security would be left to subsequent negotiations.

U.S. diplomats said the current plan is for Egypt and Israel to go to London with responses to each other's peace plan, with the United States providing compromise suggestions.

Questions over whether the London meeting could be linked to reopening of the Geneva conference came up when Sadat, interviewed on television Monday in Alexandria, said he has always been in favor of renewed Geneva talks, providing they are preceded by adequate diplomatic preparations.

A Foreign Ministry spokesman yesterday said of the proposed London meeting, "If the terms of reference are preparatory to a Geneva conference, then we will have to discuss it in the Cabinet. But if it is a meeting to begin discussing peace again, then we'll go."

Israel's caution in committing itself to a foreign minister's meeting is said by Israeli officials to stem from reluctance to appear ready and willing to discuss a peace plan that contains preconditions.

Two weeks ago, the Israeli Cabinet rejected a Sadat peace proposal without having even received it through diplomatic channels. The proposal, which called for Israeli withdrawal from the West Bank and Gaza and return of those occupied territories to Jordan and Egypt, respectively, said that negotiations for border security would be taken up after withdrawal.

Begin later denied that proposal, broadcast on Cairo radio, had been officially rejected because, he said, it was not a peace proposal at all but only an old Arab demand that had been rejected before.

Meanwhile, Dayan said yesterday that he was opposed to a meeting scheduled for Vienna early next week between Sadat and opposition Labor Party leader Shimon Peres. The meeting is to take place during the Socialist International conference.

Peres, who met Sadat last February in Salzburg, said he believed that if he were prime minister, he could reach an agreement with Sadat in a relatively short time.

Dayan was quoted on Israel Radio yesterday as saying that he believed any meeting with Sadat on the peace process should be conducted by Cabinet ministers.