War came to the center of downtown West Beirut today, sending men, women and children running for shelter along streets filled with craters and glass shards, past buildings where fires blazed out of gaping shell holes.

For many, there seemed nowhere to run on this day of terror as Israeli shells and bombs launched from land, sea and air fell nonstop from midnight until just after dark in previously spared parts of the central city, as well as on Palestinian positions in the near southern suburbs.

The pattern of the nearly 20 hours of shelling appeared to be indiscriminate to reporters and other observers who throughout the eight-week siege here have noted the previous precision of Israeli attacks. Damage spread throughout West Beirut, from once-untouched residential neighborhoods and apartment buildings, to mosques, movie theaters, banks and office buildings, from fashionable boutiques along Hamra Street, the city's commercial center, to hotels, newspapers and wire service agencies.

United Press International's office in the An Nahar newspaper building across the street from the Lebanese Information and Tourism Ministry was gutted by fire when it was struck by a phosphorous shell. The staff had taken shelter in the basement and no one was hurt.

"The Israeli Army has been ordered not to shell indiscriminately," Israeli Cabinet Secretary Dan Meridor told UPI in Jerusalem. "But if it was our shells, I am deeply sorry."

At the Commodore Hotel, where most foreign reporters in West Beirut are staying, Washington Post correspondent Jonathan Randal was sleeping in a sixth-floor room when a colleague woke him to warn of increasingly close incoming shells and suggest he move to the shelter in what was once the hotel nightclub. Ten minutes later, a shell destroyed the room two doors away of ABC television correspondent Jack Smith. Smith was in the lobby writing a story at the time.

Also hit for at least the third time, according to a Western relief worker, was the Islamic Asylum, which houses more than 500 people incapacited by mental or physical illness. The staff is down from about 100 to 15, and the facility has no water because of an Israeli cutoff, the official said. At least 10 patients have been reported killed in the past two weeks, and the children's wards on the top floor have been destroyed.

By mid-afternoon today, the American University of Beirut hospital, the largest of West Beirut's three dozen often makeshift clinics and medical centers, reported receiving 55 dead and 200 wounded. A few hours later, during a lull in the shelling and with no cease-fire in sight, state-run Beirut radio said hundreds were killed and wounded. The Christian Phalangist militia station, broadcasting from East Beirut, set the death toll in the west at 300.

At the Babir Hospital, off the devastated Corniche Mazraa and near the line of Israeli ground positions just over the Green Line separating East and West Beirut, patients have been moved into the basement. A hospital official said the already heavily damaged building took at least two more direct hits from Israeli artillery shells.

So dangerous has the hospital become that even the wounded avoid it. The official said only three injured persons were received today: one fighter and two civilians.

At 2 p.m., the Voice of Israel radio quoted an Israeli Army information officer as saying the Israelis wanted the civilian population to flee West Beirut. A Lebanese politician put it more simply: "The Israelis want us to know that nowhere in West Beirut is safe."

No reliable overall casualty figures are available for the weeks of siege, but the Western relief worker estimated that "it can't be far short of 1,000 killed" in West Beirut and its southern suburbs. He said he believed that more than 80 percent of the victims are civilians.

A major worry besides the shelling and lack of clean water is the deterioriating capabilities of rescue teams.

According to John de Salis, chief delegate of the International Committee of the Red Cross here, only 80 firemen remain working. In addition, he said, beleaguered rescue squads are running out of serviceable equipment and lack enough fuel to operate what they do have because of the Israeli blockade. When buildings collapse because of Israeli bombing or shelling, he said, it is often impossible to pull victims or survivors out of the rubble.

"How many people have died agonizingly slow deaths under the rubble in Beirut?" de Salis asked.

The horrors of the increasingly desperate conditions in West Beirut--still inhabited by as many as 500,000 Lebanese civilians who for the most part have nowhere else to go--have shocked not only those who live here, but also some of the Israeli officers laying siege, according to Western diplomats in contact with the Israelis.

"I didn't think they could do this," said one diplomatic source who lived in Israel for a year and a half. He told of confronting an Israeli officer the other day with horror stories from West Beirut, telling him, "Either your country has changed or you are making the most appalling mistakes in your history."

He said the officer answered sadly, "Maybe both."