The crossing from west to east is a maze, a distance of a few blocks that has become a convoluted series of twists and turns down dirt alleyways and once-paved residential roads filled with craters, pieces of twisted metal and blasted-out concrete chunks of apartment buildings and houses.

Much of the neighborhoods that once lined the Galerie Semaan in the southern part of West Beirut has been torn apart for a long time, victims of the 1975-76 civil war and the years of smaller battles that followed along the Green Line. Now, following yesterday's massive Israeli assault, the wreckage simply extends farther to the west and is more extensive.

West Beirut itself was quiet this morning when we left, a carload of journalists that joined the exodus to the east. At first light, residents of the besieged part of the city had emerged from basements and shelters to inspect the new damage. In the weeks since the Israeli siege began, this has become almost a ritual, one requiring a unique kind of institutional memory to distinguish the new carnage from the old.

But today, there was more to stun horrified residents than ever before. In the center of West Beirut, cars had to swerve around bomb craters, broken glass and fallen trees on a street running alongside the Jardin Publique, a park where many refugees had been camping.

Some of the worst damage was along the Corniche Mazraa, the avenue dividing the downtown area from the southern suburbs. Most of the buildings there appeared uninhabitable. Many are fire-blackened skeletons, shot to pieces even more than before in the 20 hours of almost nonstop Israeli bombardment that ended at about 8 o'clock last night.

But the worst part of the journey was near the main crossing point from east to west, an extension of the Corniche Mazraa at the national museum, the scene of heavy fighting yesterday and closed to traffic today. Immediately south of the avenue, on either side of the key road that leads to the Beirut airport, shelling and bombing have laid waste to a scenic pine forest, once the pride of West Beirut.

Heading south on the airport road, we took a left turn toward the roundabout that leads to the Galerie Semaan crossing, the only one the Israelis opened today. Instead of the Galerie, there was a large barrier of metal barrels stacked atop each other on the road. A detour to the right passed through a complex series of narrow alleys where the buildngs are all bombed out. There had not been a road here before. A car behind us was pinned down in the alleyway by sniper fire.

The first checkpoint, behind high, earthen barriers, belonged to the Palestinians' leftist Lebanese allies, who gave us and the car a cursory check and opened the trunk. The occupants of the car in front of us were obliged to give up a few little boxes of cheese and crackers. Just as the Israelis have allowed no food into West Beirut, these forces will allow none to go out.

Up ahead, back on the main Galerie Semaan road, the Lebanese Army had set up another checkpoint where a long line of cars waited and some people were walking, many with bundles of belongings on their heads. The Lebanese searched cars and carefully checked passports. The line was slow. Automobiles that leave apparently cannot come back. We left the car and driver on the western side and began to walk.

In between is a no man's land, the core of the long-blighted Green Line crossing. On the other side are the Lebanese Phalangists and the Israelis. They seemed to have little interest in our passports and gave our belongings a brief examination. An Israeli escort officer was on hand to meet the television crew that had traveled with us to carry out some tape. He asked how things were "over there."

Over here, in East Beirut, things seemed fine--the midday traffic jams were worse and the drivers were more hair-raising than ever. People were walking in the streets, shops and gas stations were open. People were having lunch in streetside cafes.

The television people had arranged for another car to pick us up on this side of the Green Line and drive us to the Hotel Alexandre, which is to the east what the Hotel Commodore is to the west--the place where most foreign journalists stay. The Alexandre, however, also has become a place frequented by Israeli soldiers, who often watch the bombardments of the west from atop the building, which sits on a hill.

Some of the Alexandre's guests had expressed concern about the presence of the soldiers in the hotel. "They've been on the roof in uniform with maps and binoculars in broad daylight," an American photographer complained. "They can be seen from the other side."

The hotel reportedly has been declared a military target by Palestinian guerrillas and Lebanese Moslem militiamen in West Beirut, although Capt. Gabriel Peled, an Israeli escort officer for visiting journalists at the hotel, said that he thought it was the press, rather than Israeli soldiers, that was targeted.

Fifteen minutes after we arrived at the Alexandre Hotel today, a huge blast blew out all the front windows. Despite the intensity of the explosion and the flying glass, no one was seriously hurt.

The charge, apparently planted in a car or a metal container next to the hotel, also set on fire a nearby apartment building and damaged about two dozen cars in the hotel parking lot, several of which had Israeli license plates.

Other explosions went off around the city, followed by sporadic small weapons fire.

Another Israeli officer, who would identify himself only as Major Ilan, his first name, said afterward he thought maybe the bombing of the hotel "could be a response" to the shelling yesterday by Israeli gunners of the Commodore Hotel in West Beirut.

Ilan said the Commodore had been "hit by mistake."