Israeli bombers and ground forces returned to the attack today as Lebanese negotiators reported they were close to reaching an agreement among U.S., Lebanese and Palestinian representatives for the peaceful withdrawal of the guerrillas from the capital.

During an intense, 45-minute air assault, an Israeli warplane destroyed a six-story apartment building that housed a Palestinian guerrilla operations room.

Reports on the number of dead ranged from a Red Cross estimate of 10 to a Palestine Liberation Organization figure of 250. Beirut radio put the death toll at 100 to 150. Many of the bodies pulled from the rubble were women and children.

The air strike hit the heart of besieged West Beirut, about 100 yards from the office of Prime Minister Shafiq Wazzan, who was absent, and about 200 yards away from where this correspondent was standing.

Rescue workers pulled out one survivor, but thereafter all of those removed from the wreckage were believed dead. Without cranes to lift huge slabs of concrete, civil defense workers were reduced to using bulldozers to remove rubble on top of the victims.

In Jerusalem, Israeli military officials announced that the air raid was in response to "repeated violations" by the PLO of cease-fire conditions.

As night fell, gunfire broke out in the southeast portion of West Beirut between Israeli and PLO forces, according to Washington Post correspondent Leon Dash, who witnessed the fighting from the roof of a hotel to the east. The fighting quickly escalated into an exchange of artillery fire as Israeli forces inched another block into the Palestinian-held western sector. Details, Page A17.

The pinpoint bombing by the Israeli warplane followed by a few hours Wazzan's claim that "virtual agreement" between negotiators had been reached on a plan to evacuate the guerrillas from the capital.

The Voice of Israel radio noted the optimism in Beirut--based on a new plan hammered out by Lebanese and Palestinian officials and reportedly praised by U.S. special envoy Philip C. Habib as constructive and positive, according to Lebanese government sources.

The Israeli broadcast then reiterated Israel's insistence that the Palestinians leave Lebanon before an international peace-keeping force be allowed to arrive.

Saudi Arabia, a close U.S. ally, issued on Friday its first implicit condemnation of American support for Israel since the Israeli invasion of Lebanon two months ago, Reuter reported. The Saudi statement did not name the United States but said, "We denounce powers supporting, backing and standing behind Israel."

During the past two weeks, the PLO has jettisoned many of its previous conditions for withdrawal. But the Palestinians and their Lebanese Moslem allies have stood firm in insisting that the international force be in place when the guerrillas leave. Otherwise, they both fear that the Israelis and their Christian Lebanese allies would take advantage of the situation.

The Israeli broadcast said that unless the guerrillas left first, the international force of American, French, Italian and Greek contingents would be used as a protective screen by the PLO allowing it to remain in Beirut. Despite the Israeli response, Lebanese Foreign Minister Fuad Boutros, who along with Prime Minister Wazzan and President Elias Sarkis conferred with Habib today, said "we are at the beginning of a road to a political solution."

"We have made progress which we hope to continue," Boutros added, "but there are some differences regarding certain subordinate points."

Government officials reported that two major remaining difficulties involved Syria's and Egypt's failure so far to agree formally to take in departing guerrillas.

The officials said the PLO has written to Syrian President Hafez Assad asking him to accept their presence in Syria. Assad reportedly had demanded such a written request to avoid later charges that Syria abandoned the fight, sold out the PLO or sought to take in the Palestinians only to muzzle their activities.

The officials said Habib hoped to convene a meeting within 48 hours of American, French and Lebanese military experts to work on the logistics of launching the evacuation plan and deploying the international force. Both the United States and France are expected to take part in the operation.

A French logistics officer arrived here today, according to the United Nations information office, to study logistics problems in having his country's force of 800 to 1,000 men act as a vanguard.

Lebanese government sources also reported that the Palestinians have dropped an earlier insistence that they withdraw their heavy weapons through Israeli lines and hand them over to the Syrian Army at the mountain village of Sofar.

Sofar marks the extreme limit of Israeli-held territory along the Beirut-Damascus road, which is to be the main exit route for the departing Palestinians.

At the scene of today's air strike, a bulldozer dug an inclined passage to the basement of the bombed building, where many of its residents were believed to have taken refuge when they heard Israeli planes overhead.

Also believed trapped in the wreckage were at least 30 officials who staffed the PLO operations room around the clock. The PLO maintains at least half a dozen operations rooms in West Beirut.

Since the Israelis trapped the guerrillas here at the end of the first week of the war, PLO leader Yasser Arafat and other senior officials have constantly changed accommodations and offices to avoid getting caught in just such an attack.

Nonetheless, rumors quickly spread that Arafat either had been in the bombed building just a half hour before the attack or was buried beneath the rubble. More than eight hours later, Arafat still had not been seen in public, but Palestinian officials insisted that he was fine.

Arafat's personal bodyguard looked on impassively at the wreckage of the building, but later told acquaintances that his parents, wife and four children lay buried beneath the rubble.

"God is against us," shrieked a distraught woman in a tiger-patterned dress and hennaed hair on the street."What can we do to destroy America?" she exclaimed, linking U.S. support for Israel to the bombing.

A car bomb later exploded outside the Lebanese Information Ministry adjacent to the prime minister's office and only 50 yards from the site of the air strike. Beirut radio said six persons died in the blast.

Today's ground fighting appeared inconclusive. The Israelis were reported to have advanced a short distance farther into West Beirut, but otherwise made no apparent gains. The Palestinians made extensive use of rocket launchers in answering an Israeli artillery barrage before a lull set in after dark.

Israeli gunboats also fired at targets in West Beirut. The targets were all within the central city's residential areas whose population has been swollen as Lebanese and Palestinians flee their homes on the periphery.

Meanwhile, Israeli Defense Minister Ariel Sharon arrived in Christian East Beirut amid speculation that he was there to oversee a 90-minute artillery duel in the museum sector where the main checkpoint in this divided capital is located.

Sharon's military vehicle got caught in traffic in East Beirut, where he was approached by a American television news reporter who asked him why he was there. According to the reporter, Sharon replied, "It's a lovely city."

News services reported these other developments:

Egyptian Ambassador Saad Mortade returned to his post in Tel Aviv and denied reports that he had been recalled to Cairo in protest over the Lebanon invasion. Egypt, the only Arab country to make peace with Israel, has sharply criticized Israel's move into Lebanon.

In Damascus, a Syrian military spokesman said that 64 Syrian soldiers had been killed or wounded Wednesday in fighting with Israeli forces in Beirut, the official Sana news agency reported.