An air of anxiety and helplessness reminiscent of the worst summer of the civil war two years ago has settled over Beirut.

The country's political leaders seem unable to come up with a formula for defusing the explosive military situation, and the patterns of the city's life - which had been well on the way back to normal - have crumbled again.

Some Lebanese say they expect a new round of full-scale fighting to erupt any minute. Others believe that the latest crisis is petering out - but that this only means the explosion they fell is inevitable has been deferred for a time.

It is hard to find anyone who foresees an early end to the country's torment.

Prominently religious leaders and politicians, for the most part the same men who were powerless to halt the catastrophe of 1975 and 1976, continue to go up the hill to the presidential palace at Baabda to urge President Elias Sarkis not to resign, fearing the chaos that might ensue.

With yesterday's announcement that a Cabinet meeting scheduled for today had been canceled, the betting was that Sarkis would not carry out his threat to step down since speculation here had his resignation following that meeting.

But privately, many Lebanese seem to agree with Beshir Gemayel, military boss of the Christian Phalangist milita, who told a Paris newspaper that it made little difference whether Sarkis stays or goes because his government "has been disintegrating for the past two years."

Sarkis, who argues that he cannot accept responsibility without power, continues to say that he wants to resign and he continues not to do it.

Political observers say the longer he leaves his resignation threat on the table, the less impact it has. The initial shock has already worn off with no sign that the Syrians or the Christian factions are going to make the concessions that would enable Sarkis to act effectively.

Syria has again issued stiff warnings to the Christian "gangs." In the words of the ruling Baathist Party's newspaper al-Baath, "Those gangs have prevented the legitimate authorities from doing their duty. To this day the authorities have not been able to develop a formula for a national army free of sectarian fanaticism. The authorities have been prevented from presenting any national accord formula because those gangs want a sectarian formula, not a national one."

The Christians, led by former President Camille Chamoun, are as defiant as the Syrians are determined. Chamoun's latest blast called the Damascus government a tool of Soviet communism.

In that atmosphere, there seemed little prospect of a breakthrough as the speaker of the Lebanese parliament, Kamel Assad, Shiite Moslem, went off to Damascus yesterday on what he called a "personal initiative."

Nor did there seem any realistic hope for adoption of a formula drafted by some prominent Christians - including newspaper publisher Ghassan Tueni and Beshir Gemayel's brother, Amin - that reportedly calls for the militias to get their weapons off the streets of East Beirut and the Syrians to pull back from the Christian area after a period of calm.

"Everybody went too far," one Lebanese observer said. "The Syrians went too far in their shelling of East Beirut. Sarkis went too far in saying he would resign. The Christians went too far in exposing their connection with the Israelis."

The reference to Israel, which has pledged itself to prevent the annihilation of the Lebanese Christians by Syria, brought up one of the great underlying fears in the present situation - that Israel woul step in, touching off a war with Syria.

As a fresh reminder of israel's interest in the current situation, Israeli warplanes streaked across southern Lebanon yesterday - creating sonic booms over the post of Sidon, some 26 miles south of here.

But there is a corollary to the fear of Israeli intervention - a deep-seated concern that if the Syrians let up on the Christian factions, the Christian leadership will push for outright partition of the country.

"They will declare their own state, you watch," a Moslem government official said of the Christians. "They have lost a lot of their territory in the northeast, but they will still do it."

Meanwhile, all flights out of Lebanon are booked full. The capital is again a divided city, with only a determined few willing to risk sniper fire to cross from the Moslem to Christian side or back. Government ministries on the Moslem side are functioning fitfully; those on the Christian or eastern side not at all.

Postal service has been out for nearly two weeks. Telephone lines were cut. Water and electric supplies have been erratic, and a heat wave has left the city breathless. The main banks are closed, as is the port.

Public transit is at a halt. It is hard to say when it will be restored, since the Christian militias used many bright new postwar buses as roadblocks during the fighting, and they are now only burned out shells.

The government has only now begun to assess the extend of the economic blow dealt to Lebanon by this latest round of fighting - the second economic bolo punch of what was supposed to be a recovery year.

The first was the Israeli invasion of southern Lebanon - hardly mentioned these days - which destroyed houses, shops and orchards, and drove thousands of refugees from their homes.