Israeli troops engaged in heavy fighting with Syrian and Palestinian forces throughout the day in the mountains east of the capital in what appeared to be an attempt to clear the Syrians out of the area between Beirut and the Bekaa Valley.

As the violence flared up, the U.S. Embassy urged all remaining Americans here to leave.

On the political front, Lebanon's newly formed National Salvation Council was reportedly trying to thrash out an agreement on what guarantees to promise the Palestinian guerrillas if they agreed to lay down their weapons. After a two-hour meeting, however, the council halted its deliberations and told the United States it could not go on with its work under the continuing Israeli bombardment.

For the first time in 11 days, Israeli jets were back in action bombing Syrian positions along the vital Beirut-to-Damascus highway and later in the day Palestinian sites on the southern edges of the city.

At 6 p.m. Israel announced another cease-fire after blaming the Syrians and Palestinians for triggering today's events by shelling Israeli positions. As of midnight, there was only sporadic firing heard in the city. The number of casualties inside the capital from the Israeli barrages earlier in the day was estimated by Lebanese police as 27 killed and 80 wounded.

Beirut radio and eyewitness accounts said Israeli troops were pushing from several points forward to reach the Damascus highway and oust the remaining Syrian forces spread out along a 20-mile stretch between the eastern outskirts of Beirut and Dhour al Baidar, on the mountain just to the west of the Bekaa Valley.

While it was impossible to tell which side had broken the already much abused cease-fire, it was clear that the Israelis were moving with calculation as their jets sought to provide coverage for several armored columns moving northward through the Chouf region southeast of the capital as well as eastward up the Damascus road.

Three key targets the Israelis are believed trying to capture were the road junction at Mderaij and the towns of Aley and Bhamdoun on the Damascus highway.

Syria has been reinforcing its forces along the highway and a recent Lebanese visitor to the Syrian capital who traveled the Damascus highway reported seeing signs of a general military mobilization just inside Syria.

The Syrians have indicated repeatedly recently that they will not accept the Israeli demand that they get out of Lebanon, and reports of their renewed mobilization and the dispatch of reinforcements seem to indicate that they are prepared for another round of fighting.

Here in Beirut, the Israelis kept up their pressure on the Palestinian guerrillas and renewed their shelling by land and sea of their camps and even hit a Lebanese Army position along the coast inside the city limits. Two Lebanese soldiers were reported killed and nine others wounded in the shelling.

Meanwhile, more eyewitness accounts by correspondents who traveled south today said the Israelis were massing tanks, armored vehicles, heavy artillery--including self-propelled 175-mm and 155-mm guns--and mobile hospitals just south of the capital.

One correspondent described the scene between Damour and Doha on the city's southern outskirts as "wall-to-wall tanks." Military analysts said the Israelis had assembled a force there far in excess of what would normally be required for an assault on West Beirut.

One theory was that the Israelis were getting ready to deploy a massive amount of tanks and armor in an attempt to crush the 5,000 to 6,000 Palestinian guerrillas trapped in West Beirut as quickly and completely as possible.

It was difficult to judge with any certainty today whether the seven-man National Salvation Council under President Elias Sarkis was really making any progress to resolve the crisis and avoid an Israeli attack on the city. From what could be learned from Lebanese sources it appeared that the key sticking point was one of guarantees for the Palestinian guerrillas should they agree to surrender their arms.

After a two-hour meeting this morning--cut short apparently by the Israeli shelling and jet raids--Prime Minister Shafiq Wazzan said that "important progress" had been made and that the committee had reached "a unified position."

He gave no further details, but it was later learned that the council had called in U.S. special envoy Philip C. Habib and told him it was impossible to continue their discussions with the Palestinians while the Israelis were shelling within sound of the presidential palace.

The council was reported to be considering a five-point plan under which the Palestinians would return to four refugee camps on the southern outskirts of the capital, the Lebanese Army would be deployed in the city and "around the camps," the Israelis would withdraw six miles from the Beirut area and the Damascus highway would be reopened. Then, in a second phase, the Lebanese government would open negotiations with the Palestine Liberation Organization for the disarming of its guerrillas.

The Palestinians were said to be reluctant to hand in their arms because of their distrust of the Lebanese Army, which they regard as little more than an extension of the Christian Lebanese militia controlled by Bashir Gemayel.

Lebanese sources close to the negotiations said one idea now under consideration was for a contingent of French troops to be deployed in the capital alongside the Lebanese Army to provide the guarantee of safety sought by the PLO in exchange for laying down their arms.

The PLO was also reported to be seeking a guarantee from the United States that Israeli forces will not try to wipe out the guerrillas if they agree to regroup in the four camps and hand over their arms.

The Palestinian demand for an Israeli pullback of six miles from the capital was partly to assure the guerrillas they would not be shelled or bombed in the camps the way they have been for 2 1/2 weeks. Since the Israelis now have artillery just south of the capital with a range well over six miles, it was not immediately clear what real significance the pullback would have as a guarantee.

Another indication that progress was had been made came from Walid Jumblatt, the Druze leader of the leftist National Movement who has been the prinicipal representative of the PLO position on the Salvation Council.

Tonight, Jumblatt told correspondents at an impromptu press conference at the Commodore Hotel that the PLO was "supporting what the council decided upon," but he added that they were still demanding guarantees.

He did not say, either, what precisely the council had agreed upon and complained bitterly about the Israeli shelling around the city, saying he refused to talk "over the sound of cannons, and I reject hot diplomacy."

"Beirut is not and will not become another Hanoi," he said earlier in the day. He was referring to the American bombing of the North Vietnamese capital in 1972 during negotiations for an end to the fighting in Indochina.

Together with Wazzan and Shiite Moslem leader Nabih Berri, Jumblatt had long talks last night with PLO leader Yasser Arafat. It was apparently at this meeting that the council came to a measure of agreement with the PLO over the plan the Palestinian leadership had proposed initially as a way out of the crisis to save West Beirut from an invasion of Israeli forces now on the southern outskirts.

The main outline of the PLO plan were disclosed in an interview with the French newspaper Le Monde Monday by Salah Khalaf, who is also known as Abu Iyad, although he did not mention the disarming of the guerrillas once they were regrouped in camps.

Whether the whole plan would be acceptable to Gemayel's Lebanese Forces was far from clear tonight. While Wazzan spoke of a unified position among the seven council members, a top aide to Gemayel, Karim Pakradouni, said they rejected the Palestinian plan for four camps "because tomorrow there would be 40 inside Beirut."

He indicated the Lebanese Forces were still pressing for a total disarmament of the Palestinians and a reduction in their status here to little more than a diplomatic one.

"There is no question of allowing a single armed Palestinian in Lebanon," he said in an interview with Washington Post correspondent Jonathan C. Randal.

The thrust of Pakradouni's thinking seemed almost identical to that of the Israeli attitude. Israel, he said, had an "international green light" to not only crush the Palestinian guerrilla movement but also "to free the world of international terrorism whose capital is Beirut."

At least three other council members were reported to share Gemayel's position, as outlined by his aide, but the Maronite Christian leader was said by one source to have decided to go along with the council plan on the assumption that the Israelis will never accept it anyway and would takes the blame for its failure.

While the council continued to discuss what Jumblatt called "an honorable settlement" and "not a total surrender" for the Palestinians, the situation on the ground threatened today to upset any progress that might be made at the negotiating table.

When the military situation appeared close to getting out of hand today, the U.S. Embassy advised the several hundred Americans still in West Beirut that it was terminating all services and urged them to leave immediately.

It said an American ship would evacuate all wishing to leave from Junieh 10 miles north of the Christian eastern sector of the city. The British and West German embassies also advised their nationals to leave.

While the French and Italian governments long since sent ships to pick up their nationals and others wishing to go, the U.S. Embassy had been reluctant to follow suit because of the political assessment that the Lebanese might make of the action, namely that the embassy expects things to get worse.