srael said today that its cease-fire in Lebanon is open-ended and that invasion forces encircling West Beirut will hold their fire unless fired upon.

Following a meeting of the Cabinet, a government spokesman also said that even if Palestinian guerrillas lay down their arms, Israel will never agree to negotiate with the Palestine Liberation Organization.

Israeli Prime Minister Menachem Begin called Sunday for an international peace-keeping force in Lebanon that he hopes will include American forces. Begin is expected to lobby for the U.S. presence in a meeting scheduled with President Reagan in Washington Monday.

Begin, speaking on "Face the Nation" (CBS, WDVM), said that Israel will leave its troops in Lebanon for as long as it takes to make sure the "scourge of terrorism" is stamped out. He denied, however, that Israel intends to seize Beirut or to capture PLO leader Yasser Arafat.

"We don't want to capture Mr. Arafat; we don't want to deal with him at all . . . . Let him go wherever he wants to," he said.

U.S. Defense Secretary Caspar W. Weinberger, appearing on "This Week With David Brinkley" (ABC, WJLA), said Reagan is reviewing the possibility of U.S. troops joining such a peace-keeping force but "a great many terms and conditions" must be set first. He also disclosed that the administration is investigating whether Israel violated U.S. law by using American-supplied arms in its invasion of Lebanon.

Israeli Defense Minister Ariel Sharon said today that Israel's "military and political objectives" will not be achieved until the PLO headquarters in Beirut is eliminated.

After a visit to Beirut to discuss strategy with the Israeli Army command there, Sharon said on Israeli radio, "Beirut is a military and political objective that we cannot allow ourselves to leave as it is today."

His remarks came as U.S. special envoy Philip C. Habib continued negotiations in an effort to avert an assault on Moslem West Beirut by the Israeli invasion forces or Christian Phalange militias. An attack on West Beirut, it is feared, would result in heavy civilian casualties.

Sharon said that Beirut is now sealed off for either PLO or Syrian infiltrators, although he said the Syrian forces are interested in maintaining the Palestinian guerrilla infrastructure there.

The defense minister said anybody who leaves his arms behind can leave West Beirut, as he said many were doing now in an effort to reach the "pacified" towns and villages of southern Lebanon. Sharon made it clear that he was talking about Lebanese and Palestinian civilians and not guerrillas.

Cabinet Secretary Dan Merridor said that the 48-hour cease-fire agreed to Friday at U.S. urging had to a "large extent" been kept. He said there have been incidents of "infringement" by the other side, and that the Israeli Army reacted with fire.

"If people fulfill this obligation not to shoot, there won't be any shooting from our side . If there will be shooting, there will be an answer. It's simple," Merridor said.

Sporadic artillery exchanges were reported near the paralyzed Beirut international airport, and Lebanese sources said firing was coming from the area around a Palestinian refugee camp that has been the scene of constant fighting between Palestinians and Lebanese Christian Phalange forces, The Associated Press reported from Beirut.

Reuter quoted the Palestinian news agency Wafa as accusing Israel of shelling coastal areas of West Beirut and the southern outskirts of the city early Monday for more than an hour.

Israeli officials said the cease-fire had overlapped another unilateral cease-fire Israel declared one week earlier and, therefore, despite the 48 hours stipulated in the agreement, there was no time limit.

The announcement came as Israeli sources said the PLO and leftist Moslem forces led by Walid Jumblatt were jointly seeking a 48-hour extension to Friday's cease-fire. But one Israeli official said the government is anxious for an early conclusion to the negotiations being conducted by Habib and is not interested in extending temporary cease-fires.

"We cannot keep having one 48-hour cease-fire after another, or one-sided cease-fires while the negotiations drag on," an Israeli official said.

Responding to reporters' questions, Merridor said Israel would not accept an arrangement under which disarming PLO guerrillas in Beirut would be conditional on Israeli-PLO negotiations.

"Israel will not negotiate ever with the organization that calls itself an organization to liberate Palestine from the Jews--ever," Merridor said. There have been reports from Beirut that former Lebanese prime minister Saeb Salam, who is acting as go-between for Habib and the PLO, proposed that in exchange for surrendering their arms, PLO leaders would be guaranteed safe conduct to Egypt where they could establish a government-in-exile.

Israel, in turn, would agree to negotiate with the PLO for autonomy of the occupied West Bank and Gaza Strip. Israeli sources said a refinement of that proposal might stipulate that the PLO be disbanded as a liberation movement but that Israel would still refuse to negotiate with the PLO under any other name.

Egypt has been actively involved in efforts to end the war in Lebanon. Following repeated appeals by the PLO, Egypt's ambassador to Israel, Saad Mortada, called on Israeli Foreign Ministry officials last week to ask for a cease-fire.

News agency reports from Cairo said that Egyptian President Hosni Mubarak welcomed the idea of a PLO government-in-exile based in Cairo. The late president Anwar Sadat had proposed such a move, which presumably would enhance Egypt's position in the Arab world.

An Israeli official said 600 people, most of them civilians, were killed in Israeli attacks on the southern Lebanese cities of Tyre and Sidon, The Associated Press reported. Reuven Shalom, aide to Economics Affairs Minister Yaacov Meridor who is coordinating relief efforts, said the casualty count was based on Israeli Army figures.

The Lebanese government has said that more than 1,100 people have been killed in Sidon alone. The military command in Tel Aviv declined to comment on Shalom's statement but was checking the number of casualties.