Druze leader Walid Jumblatt and two other prominent Lebanese figures today proclaimed a Syrian-backed opposition front to the government of President Amin Gemayel, a step that appeared to push Lebanon closer to a political partitioning.

The proclamation of a National Salvation Front, with a three-man command council and a provisional structure to handle military, financial, social and information affairs, brought the country's anti-Gemayel forces to the verge of formation of an alternative government for the large portion of the country under Syrian control.

Besides Jumblatt, the command council is to include former premier Rashid Karami, a Sunni Moslem, and former president Suleiman Franjieh, a Maronite Christian.

Political analysts here said Jumblatt appeared to be heading toward a Syrian-supported district in northern and central Lebanon that would leave the central government in control of Beirut and its suburbs and Israel the dominant presence in the south. But it was not clear whether Karami and Franjieh were willing to move as quickly toward such a partition.

Jumblatt said he was working with Libya and Syria to "foil the partition plot against Lebanon," a remark that on its face would indicate he does not see his formation of an opposition front as a separatist action.

Jumblatt, whose Druze militia has been fighting increasingly spreading battles with right-wing Christian forces in the mountains outside Beirut, held a press conference in Syrian-controlled Baalbek, 35 miles east of Beirut, to announce the new front. Then he flew in a Syrian Army helicopter to northern Lebanon, where he met with Franjieh and Karami.

In May, the three had met and announced plans for a front to oppose the Gemayel government and the U.S.-backed Lebanese-Israeli troop withdrawal agreement, but Franjieh reportedly had decided to watch developments before moving further.

Today's proclamation came a day after some of the heaviest shelling in Lebanon since the Israeli invasion a year ago, and it came as Gemayel and virtually all of the top government aides were in Washington, ending talks with U.S. officials.

Artillery and rocket bombardments of the Beirut airport and several Lebanese Army sites and Christian towns, most of it from Druze-controlled mountains, killed at least 23 people yesterday.

"After the Lebanese authorities behaved irresponsibly," Jumblatt said today, his Druze militia "were forced to strike at Lebanese Army positions and to hit Beirut airport yesterday."

"This was because all Lebanese Army positions, regretfully, are under Phalangist authority," Jumblatt said, referring to the right-wing Christian Phalangist Party of Gemayel. He said that his Druze Progressive Socialist Party followers would attack the Lebanese Army if it tried to move into traditional Druze territory in the mountains.

It was largely quiet through the day today, but scattered shelling between Druze and Christian villages was reported tonight.

Observers say it is too early to judge whether the National Salvation Front will amount to an effective secession. There is little doubt, however, that with Syrian logistical support, coupled with Libyan financing, the newly declared front would form a potent instrument of pressure against the Lebanese government.

Jumblatt, heir to the leadership of the Moslem Druze minority of about 300,000, has spent the past seven months shuttling among Syria, Libya and France as well as Jordan, and making brief trips to northern Lebanon.

Gemayel, a Maronite Christian, rose to power within the ranks of the Phalangist Party, headed by his father, Pierre Gemayel. The Druze militia and the militias of the Lebanese Forces, the Phalange-dominated grouping of Christian military units, have been locked in combat over control of the mountains for about a year.

Karami, 61, spoke to reporters at Franjieh's mountain home in Ehden, implicitly endorsing the opposition front. He skirted the details of the three-man command council and the envisioned administrative bodies.

He displayed no exceptional fervor to the creation of the front, indicating he was going along only to protect his own political interests. Karami is a prominent leader in his home of Tripoli, which is surrounded by Syrian troops that have been in constant battle with local groups that oppose a Syrian presence there.

While Jumblatt said the front's aim would be "to confront" the Gemayel government, Karami said only that he opposed "one-party" rule, meaning the Phalangist Party. He pointed out that it was Jumblatt who had "undertaken effective steps toward bringing this organization into being."

Franjieh, 71, declined to comment as he sat morosely next to Jumblatt and Karami. Outright support by the Maronite former president would be a crucial factor in legitimizing the opposition front.

Franjieh's friendship and allegiance to Damascus date to his youth, when he sought refuge in Syria after gunning down 17 people in church over a family vendetta. But there is no sign so far that he will plunge headlong into an alignment against Gemayel, despite his animosity to the president's family.

Although both Christian, the families of Franjieh and Gemayel have been rivals for years and have been on bitter terms since Franjieh's son, Tony, was killed by Phalangist gunmen in 1978 when the Phalangist militia was headed by Bashir Gemayel, Amin's brother, who was assassinated last year.

Amin Gemayel made it a point in his inaugural address in September to appease Franjieh and sought reconciliation with him. Franjieh, who described Bashir Gemayel's assassination at the time as a "pleasant surprise," has nonetheless kept his communication lines open to Amin Gemayel.

Present in Baalbek were figures from leftist and pro-Syrian factions. Among them were representatives of the Organization of Communist Action in Lebanon, the Lebanese Communist Party, the Arab Democratic Party and the National Syrian Social Party.