Foreign Minister Yitzhak Shamir, on the eve of a possibly crucial Cabinet meeting, warned today that "Israel cannot wait" much longer for Palestinian guerrillas to leave Beirut peacefully before it assaults their West Beirut stronghold.

"The Palestine Liberation Organization must leave Lebanon as soon as possible," Shamir said in an Israeli radio interview.

Shamir's remarks were seen as another effort to increase the pressure on the 5,000 to 6,000 PLO guerrillas entrenched in West Beirut and surrounded by an overwhelming force of Israeli armor, infantry and artillery threatening to close in unless the guerrillas surrender and leave Lebanon.

Prime Minister Menachem Begin's government, at the urging of Washington, has given what Begin called "a day or two" to special U.S. envoy Philip C. Habib to arrange a peaceful exit for the Palestinians. But Israeli officials for the past few days have been warning that time is running out, and Sunday's Cabinet meeting is expected to be decisive on the question of a possible Israeli attack on West Beirut.

The Cabinet had been scheduled to meet Thursday in what was expected to be a key session. After a visit to Jerusalem by U.S. Deputy Assistant Secretary of State Morris Draper, however, the session was put off. This was interpreted in the Israeli capital as a response to requests by the United States that more time be given to Habib for his negotiations in Beirut.

The Army chief of staff, Maj. Gen. Rafael Eitan, has indicated that Israel could resort to military moves on a lesser scale than an all-out attack on Beirut, which would be likely to cause many civilian casualties. Eitan did not specify what these moves would be, but some Israeli officials have spoken of commando raids directed at specific Palestinian targets. A week ago, Israeli warplanes bombed Palestinian-held areas, including civilian neighborhoods, and Israeli artillery and gunboats shelled the area heavily.

"A military solution can be reached in Beirut without going into the crowded quarters of the city," Eitan said in a weekend interview with the newspaper Maariv. "There are three ways of getting the terrorists out of Beirut. The first is via negotiations, and we are in the throes of this process. The terrorists have been given an opportunity to leave peacefully, by land or sea. The second way is military, and the third is a combination of both."

Shamir, in what seemed to be a reference to PLO demands for a political presence in Lebanon, rejected any distinction between the group's military and political activities--which he lumped together as terrorism. The distinction, he said, is "an invention of the West, Europe, perhaps of France."

President Francois Mitterrand's government in Paris has launched an initiative in recent days to avert an Israeli attack on West Beirut, underlining its traditional ties with Lebanon and its belief that the PLO is a legitimate representative of Palestinian national aspirations. This is anathema to the Israeli leadership, which has vowed to crush the PLO as a political as well as a military force, claiming that only then will the Camp David autonomy talks have a chance of success.

Despite indications that the United States has been pressuring Begin to hold off on attacking Beirut, Shamir said U.S. policy has not changed since Secretary of State Alexander M. Haig Jr. resigned. The Israeli minister described the U.S. attitude before and after Haig's announcement as "a policy of friendliness and understanding."

Shamir dismissed signs of limited public dissatisfaction with the Begin government's conduct of the war, calling them the crying of "fringe groups" that do not reflect the country's genuine public opinion. The government, he added, will ignore the complaints and continue to make decisions according to its assessment of the national interest.

A demonstration organized to protest the war drew between 7,000 and 10,000 people tonight in one of Tel Aviv's main squares, according to estimates by journalists. Mainly young people enjoying the balmy Mediterranean evening, the protesters shouted slogans, waved signs proclaiming "no more wars like this" and listened to antiwar speeches in an atmosphere reminiscent of the anti-Vietnam War protests in the United States.

"Sharon has to go," shouted a soldier from a tank unit that fought near Damur in Lebanon, referring to Defense Minister Ariel Sharon. "He has broken the faith of the soldiers. No more wars without a national consensus. The strength of Israel is its unity, even with differences of opinion. But this war is going to kill that unity."

While the peace protesters demonstrated in the city center, tens of thousands of Israelis--at least twice as many as attended the peace rally- strolled through an exhibit of captured Palestinian and Syrian weapons at a suburban fairgrounds.

"This is the real people," an Army officer said as families walked through the lined-up Syrian T62 tanks and the PLO's multiple rocket launchers mounted on trucks.

The exhibit was organized by the government to underline its contention that PLO arms stores were immense, justifying the invasion launched four weeks ago Sunday. Stacks of ammunition crates were on display, along with 130-mm cannons and a variety of PLO arms and equipment ranging from rocket-propelled grenade launchers all the way down to IBM typewriters from guerrilla offices.

"It's crazy," said Iris Kitlin, 25, of Tel Aviv. "I was curious, so I came. "But it's unnecessary. We had to go to war because otherwise they would have got us, as all this stuff shows."

The Jerusalem Post newspaper, apparently confirming the impression gathered from tonight's crowds, published a poll yesterday showing that 76 percent of those questioned backed the invasion of Lebanon without reservation