The Lebanese government and the leadership of the Palestine Liberation Organization officially approved a U.S.-mediated agreement today aimed at starting the evacuation of PLO guerrillas from West Beirut.

In Jerusalem, the Israeli government received the final version of the plan and scheduled a special Cabinet meeting Thursday to consider it, Washington Post correspondent Edward Walsh reported.

Israeli radio said tonight that the government of Prime Minister Menachem Begin is expected to approve the plan at Thursday's meeting, and the report added that the withdrawal should begin Saturday.

The long-awaited approval was announced by Lebanese Prime Minister Shafiq Wazzan after a three-hour meeting of the Lebanese Cabinet held at the palace of President Elias Sarkis at Baabda, five miles east of the embattled capital.

"The Cabinet agreed to the plan, which we prepared with U.S. special envoy Philip C. Habib for the departure of the Palestinians from the capital, Beirut," Wazzan said after the Cabinet meeting. The prime minister said the government's approval was based on its understanding that Israel already had told Habib it was in agreement with the details of the accord.

The PLO leadership had given its own backing to the plan earlier in the day after final negotiations with Habib through Wazzan.

Foreign Minister Fuad Boutros said he hoped the plan would be able to be set in motion either Saturday or Sunday, although Wazzan is to announce the exact schedule within 24 hours, or after Israel's official acceptance.

The accord was nailed down, according to PLO sources, after the organization agreed to Israeli demands that it free a captured Israeli pilot, Lt. Aharon Ahiaz, its lone prisoner of war since Israel's invasion of Lebanon June 6.

The PLO reportedly agreed to turn over the pilot to Wazzan in West Beirut, who will then drive him to East Beirut and turn him over to U.S. officials. They in turn will release him to the Israelis.

The PLO also will turn over to Lebanese authorities the bodies of five Israeli soldiers killed in the invasion and will provide information about the location of a cemetery outside a small Christian village in the Israeli-occupied south of the country where four other Israeli soldiers, killed in an earlier Israeli invasion in 1978, were buried.

Along with that final PLO concession, Habib was reported to have a written Syrian commitment, through the Lebanese government, that Syria would agree to the withdrawal of its own forces in West Beirut. These comprise 5,000 Syrian and Palestinian soldiers who formed an integral part of the Syrian Army's Arab Deterrent Force, which had sought to police Lebanon under a now-expired Arab League mandate since the end of the 1976 civil war.

The agreement on the Habib plan, however, did not halt the violence in the war-weary western sector of the city, which has been under siege by the Israeli Army for almost 10 weeks. Tonight, a six-day calm was broken by a string of explosions apparently set off by the PLO when it sought to defuse a car loaded with rockets and TNT parked near the offices of the Palestine Research Center, a PLO think tank, in West Beirut.

The explosions left cars burning in the streets, and the rockets went off in a series of secondary blasts that showered the night sky with balls of fire. Several persons were reported to have been wounded by the explosions.

The blasts came on the heels of a brief fire fight around the Villa Mansour, the Lebanese parliament building that has been turned over to the Lebanese Army by the Israelis today in anticipation of a meeting Thursday of Lebanon's 92-member legislature. The deputies were supposed to try to select a successor to Sarkis, whose six-year term expires Sept. 23, but the meeting was postponed tonight by the parliament's speaker because of the "deteriorating security situation."

Radio Lebanon reported that the shooting around the parliament was between the Lebanese Army, which took up positions around the building after the Israelis pulled back, and Moslem militiamen just across the National Museum crossing point between the city's divided Christian and Moslem sectors.

Meanwhile, Israeli military officials announced that two Israeli soldiers were killed and four wounded in a PLO ambush east of Beirut last night, correspondent Walsh reported.

The officials also said there were clashes between Israeli soldiers and the guerrillas today in eastern Lebanon and northeast of the coastal city of Sidon in which three Palestinians were killed and five captured. Israeli forces suffered no casualties, the officials said.

None of the incidents appeared to have provoked retaliatory actions today of the kind that have shattered past cease-fire accords.

Lebanese officials said they hoped the agreement to evacuate some 7,100 PLO guerrillas and another 5,000 Syrian-led soldiers of the Palestine Liberation Army and its own remaining contingents in the Lebanese capital would be just the first phase of the eventual withdrawal from the rest of the country of all foreign troops -- Palestinian, Syrian and Israeli.

Boutros is expected to set the Beirut evacuation plan rolling Thursday by submitting a formal request to the governments of France, Italy and the United States for an international military force--expected to number about 2,150 men -- to guarantee the PLO withdrawal from the Lebanese capital.

A group of 800 U.S. Marines that will make up part of the force is already at sea in the Mediterranean steaming toward Lebanon. Meanwhile, a vanguard of 350 French paratroopers was being readied to fly to Cyprus tonight to board French troopships that should arrive at the Lebanese Christian port of Juniyah, about 11 miles north of Beirut, by Friday.

Sources close to the PLO said this French force will take up positions in the port of Beirut either Saturday or Sunday after an initial Israeli pullback. On the same day that the French paratroopers enter the port, chartered ships, under U.S. Navy protection, will arrive to begin loading the first of the PLO evacuees who will be allowed, according to the agreement, to leave with their personal weapons. The PLO evacuees will sail to Cyprus the same day and disperse from there.

A spokesman for the Red Cross said that Israel had agreed to allow 20,000 liters of fuel and 40 tons of emergency food to enter West Beirut in what would be a major relaxation of the siege of the Lebanese capital, United Press International reported.

Correspondent Walsh added from Jerusalem:

Israeli radio said that Israel "will make every effort to see that all PLO members are photographed" as they leave the city by the multinational force.

The withdrawal plan was forwarded to Begin shortly after Israeli officials said there were still three "serious" but not insurmountable problems to be resolved.

The problems, the officials said, included the lack thus far of a firm commitment from Syria that the Syrian troops and the members of the Palestine Liberation Army attached to Syrian forces will also leave the capital and all of Lebanon.

The officials said Israel was also waiting for a written pledge from France that its troops will leave Beirut if the PLO refuses to leave the city or reneges on its other promises in the accord.