Her lips are swollen and blackened, her thin frame swathed in ointment-soaked gauze. From her bed in a makeshift hospital at International College here, she recalls when the shell hit the underground garage where she and her family were hiding a week ago.

"Everything suddenly went dark," says 17-year-old Fatmeh Aytawi, "and then I remember a brilliant white flame, and I felt I was suddenly on fire."

Hours later, when rescue workers finally dug the Aytawi family out of the rubble and rushed them to the hospital, doctors recall that their bodies were still smoldering. Fatmeh's mother died last Monday, while her father remains in serious condition. Four sisters and a brother also are hospitalized.

Doctors here and at hospitals throughout West Beirut say they are seeing an increasing number of burn patients like Aytawi and her seven family members, who they say are victims of Israeli phosphorus shells that were part of the intense bombardment that rained down on the Lebanese capital in recent weeks.

The wounds are distinctive and much harder to treat than ordinary burns, the doctors say, in part because phosphorus sticks to the skin and can burn for hours. It cannot be extinguished by water, which causes a chemical reaction that makes the wound burn more. Like the Aytawi family, victims often arrive at the hospital with smoke still pouring out of their bodies from internal burns as well as skin injuries.

Israeli authorities say they only use the shells as "markers" to guide artillery because the smoke the shells give off helps gunners zero in on their targets. The Israelis say phosphorus shells traditionally have been used in this fashion since World War II and blame civilian injuries on Palestinian guerrillas who chose to make their stand in civilian-occupied parts of the city.

With the chaos that the two-month Israeli siege and bombardment has produced here, it is impossible to determine exactly how many civilians have been killed, maimed or, like Aytawi, disfigured by Israeli phosphorus shells. Still, many doctors say the number of burn cases they have seen has increased markedly this month, which corresponds with the first physical evidence of heavy use of phosphorus shells.

"Most of the serious injuries we were getting during the early part of the war were from bullets and shrapnel," said Sameer Shehadi, chief of surgery at the American University of Beirut's teaching hospital here. "In the last two or three weeks, though, we have been getting a number of serious burn patients."

Dr. Amal Shamma, the U.S.-trained, Lebanese director of the now-closed and shell-battered Barbir Hospital, recalled when one couple brought in three small children -- two dead, 5-day-old baby girls and a badly burned 3-year-old boy, all of whose bodies were still smoldering. The boy died the next day.

Troy Rusli, a Cambodian-born, Norwegian doctor who is a volunteer surgeon at the makeshift Lahout Hospital at West Beirut's Near East Theological Center, described a man, about 60, who was brought in with a piece of phosphorus-coated shrapnel lodged in his chest.

"Smoke from the burning phosphorus inside him was coming out his nose and mouth with every painful breath," recalled Rusli. "We had to cut the shrapnel out of him before we could finally stop the burning by cutting away the scorched tissues."

"No weapon is a good weapon," said John Barton, an Illinois University professor of medicine who is working as a volunteer at the same hopsital. "But this one, the phosphorus bomb, is one of the worst."

Shamma said most hospitals lacked both the supplies and the expertise to treat phosphorus victims properly. She said doctors were relying mostly on printed information compiled by U.S. military doctors in Vietnam and on a handbook of war surgery published by the North Atlantic Treaty Organization.

There is no way to determine accurately how many phosporus shells have been dropped on this city. But dozens of 155-mm artillery shells dug from the rubble of the main Palestinian neighborhoods on Beirut's southern fringes have hollowed interiors coated with yellowish-orange oxide, and the pungent odor of phosphorus is unmistakable.

Other phosphorus shells have hit the city's center in the vicinity of the Hamra Street business district. One gutted the offices of Newsweek and the Los Angeles Times in the An Nahar newspaper building minutes after correspondents had left to seek refuge in the building's basement. At least two of the city's 19 hospitals also have reported being hit with the shells.

Some doctors, especially those who have not treated phosphorus-burn patients firsthand, are reluctant to estimate their number, saying pressure on hospital laboratories have made chemical analyses impossible. All burn victims generally are treated alike here after surgery, and medical records often do not distinguish phosphorus victims from other burn patients.

Joseph Ayyad, a Palestinian of Spanish citizenship who is Aytawi's doctor, said he is treating 17 phosphorus-burn patients, 11 of them civilians.

It was unclear Thursday whether the shells are Israeli- or American-made. Benjamin Abileh, an Israeli Embassy spokesman in Washington, said he could not provide an answer, but noted that the shells "have been made all over the world for many years and used in all the armies of the world for many, many years."

Abileh acknowledged that the phosphorus shells could cause severe injuries but said they were less deadly than regular artillery shells. "People can get burned, but with another kind of shell they would die, so in this sense it's a less dangerous weapon," he said.

A Department of Defense spokesman said the Pentagon was checking to determine whether U.S.-made phosphorus shells had been sold to Israel. He said that unlike the special, classified restrictions on Israeli use of U.S. cluster bombs, the only restriction on phosphorus-shell use would be the provisions of the Arms Export Control Act that require that American-made weapons be used only for defensive purposes. Israel has argued that its invasion of Lebanon was undertaken in self-defense.