Israel today carried out its heaviest shelling in a week, hitting buildings in West Beirut's fashionable shopping area and Palestinian refugee camps as well as a hospital and the Soviet Embassy compound.

Although the damage to the Soviet Embassy appeared to be minor, the attack brought a bitter denunciation from Moscow. The Soviet news agency Tass reported that the shell caused damage within the embassy compound but did not give any details.

"The Israeli government, which is flouting generally recognized international legal norms, bears full responsibility for such criminal actions by Israeli troops, which have intruded in the territory of Lebanon," Tass said.

But in Tel Aviv, the Israeli high command denied that its forces were responsible for shelling the Soviet Embassy, Reuter reported. "Our forces did not fire in the direction or in the area of the Soviet Embassy in Beirut," an Army spokesman said. "If any damage was caused to the Soviet Embassy, it must have been as a result of firing from Syrian positions, which were observed firing in that direction."

Syria, which is seeking to stem its losses from the Israeli invasion, has asked the Soviet Union for a "strategic cooperation" pact that would provide more advanced Soviet weapons.

There were no clear casualty totals from the renewed Israeli attacks today. The Palestinian news agency Wafa listed Palestinian causalties as "heavy" and the right-wing Voice of Lebanon Radio said 20 Lebanese were killed and 57 wounded.

The renewed shelling, which has been limited so far to inside the city limits, and the implied threat of a greater Israeli push appeared to be a calculated Israeli effort to cause a split between the Palestinian guerrillas and their leftist Lebanese allies trapped in the predominantly Moslem western sector of the capital. Also implicit was an Israeli signal that unless the newly formed National Salvation Council acted quickly to disarm the Palestinians, the Israelis still had every intention of launching a ground assault against the guerrillas.

The council, a group of Lebanon's seven main political and military leaders, met for the first time yesterday and set another meeting for Tuesday. Political analysts had speculated that the meeting of the political rivals yesterday was part of a broader agreement to find a solution to the crisis. But the council's failure to do anything beyond scheduling another meeting evaporated hopes that there was any consensus and contributed to the rise in tension.

Despite evidence of growing Palestinian isolation, the PLO rejected calls for surrender and vowed to "defend . . . the honor of Beirut."

The Israeli artillery and naval gunfire started soon after midnight and continued sporadically throughout the day in an apparent effort to soften Palestinian defenses around Sabra, Shatipa and the Bourj el-Brajneh refugee camps in the southern outskirts of the city. Each side accused the other of responsibility for the major rupture in a cease-fire between Israeli and Palestinian forces that was first agreed to on June 12 but had broken down several times previously.

Lebanese reports suggested the Israelis ordered the artillery, armor and naval bombardment in reprisal for the ambush of an Israeli infantry patrol near a mountain village 20 miles southeast of Beirut, The Associated Press reported.

Acre hospital, located on the southern end of town, suffered 13 direct hits--and five other rounds landed nearby, according to correspondents who visited the facility run by the Palestine Red Crescent. Six patients were reported killed and nine wounded.

Palestinian officials said that besides landing on the Soviet Embassy grounds, shells hit the Bourj Abu Haidar working-class district and Army barracks on the Corniche Mazraa, which is the undeclared dividing line between supposedly "safe" West Beirut and the Palestinian area to the south.

AP correspondent Alex Efty visited the Soviet Embassy after the attack and reported little damage. He said the shell knocked a few branches off a tree on the edge of the embassy compound but did no other apparent damage.

Ramlet el Beida, once a fashionable residential area facing the Mediterranean also south of that line, and Raouche, which is the continuation of Corniche Mazraa, came under Israeli gunfire. So, too, did Hamra, the once most elegant shopping district in the Arab world, where several rounds landed.

One round landed around the corner from the Commodore Hotel, Beirut's press center since the 1975-1976 civil war.

Meanwhile, five American reporters were picked up and held for 2 1/2 hours while being questioned by leftist Lebanese militia. They were released unharmed with the explanation that Palestinians fear that Israel has infiltrated agents into the city.

The five were David B. Ottaway of The Washington Post, William E. Farrell of The New York Times, David Lamb of the Los Angeles Times, Daniel William of the Miami Herald and Timothy McNulty of the Chicago Tribune.

Speaking to ABC and Visnews television, PLO leader Yasser Arafat today charged that "the Israelis, in close cooperation with the Pentagon, are preparing to commence their attack on Beirut." Noting that "Beirut is the first Arab capital" under Israeli siege, he echoed many Western diplomats' concerns in warning that the American "government will pay the price for what has been done because you have already destroyed all your interests in the area."

He was developing a familiar Palestinian theme that the crushing of the PLO and the occupation of an Arab capital could dangerously undermine pro-Western Arab governments such as Saudi Arabia and other oil-producing conservative Persian Gulf states.

Against this background of mounting pressure and tension, Arafat held a series of meetings with Prime Minister Shafiq Wazzan, and former prime minister Saeb Salam and other Lebanese political figures to prepare for the meeting of the National Salvation Council.

Special American envoy Philip C. Habib conferred with President Elias Sarkis, Wazzan and Foreign Minister Faud Boutros in yet another effort to hammer out a joint Lebanese position and define the guarantees required to persuade the Palestinians to accept a political compromise involving surrendering their arms and sending the Lebanese Army into West Beirut.

Reflecting confusion in Palestinian ranks, Yasser Abed Rabbo, an official of the PLO, said the leadership had "rejected" U.S. demands to surrender their arms and would "fight everywhere to defend the revolution and the honor of Beirut."

For the first time there were visible signs that the Israeli tactics to pressure the Palestinians and drive them out of Lebanon were having some effect. Pressed by Moslem politicians fearful of heavy civilian casualties among the western sector's remaining half million residents, Salah Khalaf, a close aide to Arafat, said in an interview with Le Monde, "If there was no other solution, we will propose to the Lebanese leaving West Beirut and regrouping our forces in the camps so as not to be held responsible for the city's destruction."

While Khalaf's proposals to return to the exposed camps on the outskirts seemed militarily suicidal, it underlined the Palestinians' growing realization of their isolation even among their long-time Lebanese Moslem allies. Military specialists had expected the estimated 5,000 to 6,000 Palestinian guerrillas to fight a hit-and-run battle throughout West Beirut to inflict maximum casualties on the Israelis rather than regroup in their camps and expose themselves to superior Israeli firepower.

Israel continued its massive buildup of tanks and other armor in and around the 10-square-mile redoubt of West Beirut. One eyewitness reported seeing a column of 70 tanks moving north toward the Khalde road junction just south of the airport in the southern suburbs.

Ground fighting was reported at Jamhour, where the Israelis were credited with knocking out four Syrian tanks guarding the vital Beirut-Damascus highway near the presidential palace at Baabda.