The cease-fire arranged last night by U.S. Middle East envoy Philip C. Habib held throughout today in Beirut, and Lebanese and Palestinians took advantage of the pause to bury their dead after two days of a massive Israeli bombardment of the western sector of the capital.

Casualties were reported by the conservative newspaper An Nahar to be 300 dead and wounded, while other press reports put them as high as 2,000.

The cease-fire, the fourth called since the Israeli invasion of Lebanon began three weeks ago, was the first actually to take hold and brought renewed hope that a way could be found to avert the threatened Israeli assault on West Beirut.

Eyewitnesses said, however, that the Israelis were using the pause to reinforce their positions around the Beirut airport and the Palestinian camps on the southern outskirts of the city. The Syrians, who took a beating along the vital Beirut-Damascus highway this week, also were reported to be reinforcing their remaining positions in the eastern Bekaa Valley.

The only major cease-fire violation that was reported took place outside the capital in the Bekaa Valley, where early this morning Israeli jets attacked what an Israeli government communique called a new Syrian SA6 surface-to-air missile battery and destroyed it. Reports reaching here said that there are now two Syrian divisions in the valley just north of the Beirut-Damascus highway between Zahle and Riyaq, site of a major Lebanese air base.

The U.S.-engineered lull in the fighting followed reports that Saudi Arabia had put strong pressure on Washington to urge Israel to stop its shelling and bombing. Saudi King Fahd sent a telegram to President Reagan today saying it was "necessary" to halt Israel's "barbaric" invasion of Lebanon, according to an official Saudi press agency report quoted by Reuter. "What Israel is doing will lead to serious consequences for peace in the region and the whole world," Fahd said.

Habib was reported to have immediately taken advantage of the halt in hostilities to present to President Elias Sarkis a new set of American proposals regarding the Israeli, and apparently American, demand for a disarmament of the Palestinian guerrillas inside Lebanon. This movement on the diplomatic front came as Prime Minister Shafiq Wazzan, who handed in his resignation to Sarkis yesterday, was reported ready to withdraw it and return to head the paralyzed government.

These two events, against the background of a cease-fire, moved former prime minister Saeb Salam, a key mediator in the current crisis, to remark, "Things are looking better."

"There's been a new development," Salam told reporters at his home tonight. "Maybe there could be a new assessment."

Salam said Wazzan was now ready to resume his duties as prime minister, but there was no confirmation of this from the leader himself.

Wazzan, Salam said, had already acted to turn over the new American proposals to leaders of the Palestine Liberation Organization for their consideration.

Despite these developments, PLO officials cautioned that Lebanon was still in "a state of no war and no peace" and predicted "a tough few days ahead" while efforts continued to find a formula acceptable to both the Palestinians and Israelis to disengage their forces.

"There is no real cease-fire without the interposition of a neutral force," remarked one official, who also expressed concern about U.S. leadership as a result of the temporary vacuum at the State Department following the resignation of Secretary of State Alexander M. Haig Jr.

Meanwhile, Dr. Fathi Arafat, head of the Palestinian Red Crescent and brother of the PLO chairman, said in a news conference today that the heavy Israeli use of "fragmentation, cluster and phosphoric bombs" was inflicting heavy psychological damage on those Beirut residents who were not directly hit during the bombing.

Pictures in the Lebanese press this week, sometimes covering three to four pages, showed gruesome details of small babies burned by phosphorus shells or wounded elderly people unable to flee from the wave of attacks.

According to Arafat, the number of dead and wounded during the past 23 days in Lebanon has risen to 35,000, with 2,000 in Beirut alone in the past four or five days.

The Lebanese Red Cross early in the invasion published figures indicating that 1,200 persons died in Sidon alone, but Israel has challenged those figures and others out of Beirut and claimed casualties have been much lower.

Arafat charged that Israel had violated the Geneva agreement on the conduct of warfare by using "all kinds of new weapons" against Lebanon during the Past three weeks. Doctors in the Lebanese Barbir Hospital and the Palestinian-run Gaza Hospital have said that most of their patients had suffered from cluster bomb wounds and phosphorus shells.

At the Gaza Hospital Friday, before it was hit by Israeli bombing and evacuated, were seven patients with purple burns covering their upper torsos, faces and arms.

Dr. Michel Lariviere, president of the French-Palestinian medical association and part of a French medical team inspecting hospitals and damage here, said West Beirut and its southeastern outskirts reminded him of Coventry, England, after it was bombed in World War II.

Lariviere, who spoke after Arafat, told journalists that his medical and military experience convinced him of two distinct patterns in Israeli attacks against Beirut. "One pattern was the use of big caliber bombs directed at buildings believed to house PLO officials, but another pattern is a concentrated use of antipersonnel bombs aimed at individuals," he said.

The second kind of attack, using cluster, fragmentation and incendiary shells seemed to prepare the way for the invasion by infantry and tanks, Lariviere said.

He said such tactics might be designed to keep key roads into the capital and inside it intact for tanks rather than having them blocked by rubble.

Lariviere, who was accompanied by Lucien Bitterlin, president of the French-Arab Solidarity Association, and two Norwegian doctors working in the Gaza Hospital, said the group witnessed an intense Israeli bombing raid that forced the evacuation of the hospital. The Gaza Hospital is situated inside the Palestinian refugee camp of Bourj Barajneh.

Heger said 50 patients had died during operations in the past 48 hours, "some because the pressure just destroyed their lungs." As he started on another patient, the Norwegian doctor said the administration decided to evacuate the hospital. "Most of us went downstairs, but patients who could not be moved, who were in traction, remained in their beds listening to the bombs and the planes," he said. "Many of them were wounded for a second time."

Norwegian surgeon Dr. Hans Husum spoke about what is now being referred to as the "Begin amputation," referring to wounds caused by "high-energy and high-velocity projectiles or pellets" produced by fragmentation bombs.

"I received a patient with what appeared like a bad wound on his foot; the skin on his leg looked fine, but underneath the muscles and bones were completely destroyed," the Norwegian doctor said. "I had to amputate his leg all the way to his knee." Several such operations have been performed at Gaza Hospital over the past week, he claimed.

Husum said that there was a "very high mortality rate" during operations.