After so many thousands of casualties and six years of war, it was a day to mourn the passing of trees in a garden that once was a symbol of calm in the Lebanese capital.

The dead get buried, their martyrdom only briefly memorialized in posters that soon peel in the damp climate of this Mediterranean port. And so it is that the visible decline of this city is dramatized more by its physical destruction than by the toll in lives -- more so by the violence done to its natural beauty than to its man-made buildings.

Relatively untouched in all the previous rounds of fighting, the Bustros family's graceful Ottoman mansion in Christian East Beirut was badly scarred by the missiles that Syrian gunners fired at random last Thursday.

None of the family or its retainers was hurt. But opaline and Sevres vases were shattered.Much of the glass and some chandeliers were destroyed in the shelling, which also blew out the kitchen doors, scarred the outside stone walls and damaged cars parked on the premises.

Yet the most poignant devastation was in the backyard, once a paradisiacal retreat from the world protected by a high stone fence and overreaching trees that blotted out the Mediterranean sky.

The missiles ripped a hole in the wall and most of the trees are down, perhaps a lesson that such calm has no right to exist in Beirut anymore.

As for the Lebanese -- especially the Christians of East Beirut who are once again under Syrian guns -- the crises have blurred into such a murky continuum since 1975 that they have developed a nonchalant shorthand for survival.

Capsulized verities at times seem to reduce life to a series of one-liners. For instance, Bechir Gemayel, the commander of Christian forces now in their second week of fighting the Syrians, announced, "The United States is handling the Arab world to the Russians on a platter."

Dressed in boots and khaki uniform as befits his office, Gemayel brushed aside Secretary of State Alexander M. Haig Jr.'s recent remarks condemning the Syrians in the current round of Lebanese fighting.

At face value his attitude was surprising since the Christian militias vainly had sought just that unequivocal American support since the fighting first erupted six years ago.

Gemayel climbed the steps at his waterfront military control headquarters. Syrian artillery had shelled the already battered area this morning for the first time in this round of fighting, only hours before yet another cease-fire was announced.

Gemayel's sibylline words were not just those of a leader intent on maintaining a sense of mystery. They are echoed in every family, recited with variations to pass the time between playing cards or listening to the radio news.

"The Americans won't really come," a mother said to her four grownup children, "nor will the Israelis."

"Do you think it's true that there's been a deal -- we are going to be divided up between the Syrians who will keep the Bekaa Valley in the east and the Syrians and Palestinians who'll take the south?" asked the eldest daughter.

"What does Haig really mean? Will he really let the Israelis come and help us?" the son asked.

"The Israelis just talk about saving us," the second daughter said, "but they want to keep the situation as it is, turning the faucet of violence on and off when they want."

"We don't see the end of all this," the mother sighed. "We hope the Americans or the Israelis or the Martians will get rid of the Syrians for us, but we don't really believe it anymore."

All these ideas are thrown out helter-skelter. No rational discussion ensues, largely because over the years too many arguments have solved nothing.

Lapidary, headline-like statements have become a kind of game, a way of getting through the bad days.

In the hall of the apartment a family has dumped its suitcases, ready to take down to the cellar in case the fighting gets too dangerous . Desultroy small-arms fire and the fairly distant thump of artillery are audible.

The guests go out on the eighth-floor terrace to watch the black smoke rising from Army installations, the most recent target for Syrian gunners along the "green line" dividing Christian East Beirut from its predominantly Moslem western part.

Streets are empty save for stray cats, rushing ambulances and nonchalant militiamen playing paddle ball despite their flack jackets.

The family spend most of the morning in the cellar, but had returned. Years of war had taught the children not to use elevators because the electricity could go off, trapping them between floors, and because the elevator shafts are relatively unprotected from shelling.

"You cannot spend your life in the shelters," the mother says. "And anyhow, it's bad for the complexion."

"It's only the very rich and the very poor who stay here," mused a banker who had taken a shortcut to return from West Beirut in the morning.

The banker approvingly quoted Pierre Gemayel, Bechir's father. "God knows I rarely ever agree with him, but today he got something right. He said, "The Jews were kicked out and it took them 2,000 years to get back. The Palestinians were kicked out and they're still fighting to get back. We, the Maronite Christians who are the backbone of this country, have been here 1,300 years and we'll fight to the last drop of blood rather than give up.'"

Such talk buoys the weary and the brave, those who have stayed and endured, those who no longer spend long hours on the telephone calling each other to explain every shell and every violent death as they did back in 1975 when Beirut still considered itself the most civilized city in the Third World.

Indeed, violent death has become as natural and accepted as the mass exodus that ensured last Thursday after Syrian gunners shelled East Beirut for four hours -- without the usual telltale escalatory steps more orderly departures.