Phosphorous bombs have become the napalm of the war in Lebanon

What napalm was to the Vietnam war phosphorus is to the war in Lebanon, particularly in Beirut.

And the use of phosphorous bombs against human targets - civilians as well as soldiers - has begun to raise new questions about the United States arms trade to the Middle East. It does so, ironically, even as the siege of Beirut seems near an end.

Earlier in the war a muted crisis arose between President Reagan and Israeli Prime Minister Begin over Israeli use of US-supplied cluster bombs. That dispute ended in a temporary cutoff of shipments of the bombs to Israel.

Diplomats and hospital personnel here are beginning to go public with evidence of the widespread human damage caused by the phosphorous explosives. The result is likely to be renewed questioning as to why Washington fails to enforce the defensive-only restriction it places on use of such exported weapons.

''Phosphorus is a more sophisticated kind of napalm. It is designed to strike military installations like fuel depots. . . . It is antipersonnel,'' said Dr. Amir Salam, a urologist working at the American University Hospital.

In west Beirut, phosphorous shells and bombs have crashed onto the main street, Hamra, hitting banks, local newspapers, and foreign news offices. They have plowed into two hospitals, a Red Cross building, and hundreds of apartments.

The Palestinians do not have phosphorous weapons. Those used in the city have crashed into areas where Palestinian civilians had taken refuge, such as Hamra.

There are no precise, reliable figures for any aspect of the war yet, including the number of burn cases. But doctors said they have treated hundreds - at the very least.

Dr. Salam said neither he nor any of his colleagues here are burn specialists.

''Unfortunately we are guessing on the treatment. We don't have time to research it. We rarely have time to do much more than amputate,'' Dr. Troy Rusli said. Dr. Rusli, who worked in Cambodia but lives in Norway, said he treated about 50 cases in five weeks. His ''hospital'' is the basement garage of the Near East School of Theology.

The use of phosphorous bombs by the Israeli Army has been condemned by relief workers in Lebanon who have seen its effects. They say that without the proper supplies, the only way to stop the burning is either to cut the burning tissue away or amputate. No one here has the supplies.

Relief workers are reporting an unusually high incidence of amputations in west Beirut - particularly, they say, among civilians. Phosphorus reportedly continues to burn for up to 24 hours unless treated.

The American University Hospital, Beirut's best, said it had received hundreds of burn cases. Staff in the emergency room estimated 80 percent were civilians and 20 percent guerrillas. One Palestinian Red Crescent Society field hospital said its phosphorous cases were split 50-50 between guerrillas and civilians. Several other hospitals said their breakdown was about 70 percent civilian and 30 percent guerrilla.

Ahmad Abdisaleh, an elderly Palestinian porter who lived in Borj el Barajneh, was eating breakfast when a phosphorous shell smashed through his house.

Phosphorus, a yellowish powder, sprays out of the shell casing, igniting instantly when it hits air. Mr. Abdisaleh's body and clothing went up in flames.

At first glance, Mohammed Halil, another patient who is a PLO guerrilla, looked Sudanese or Ethiopian. His face was black. But when a doctor pulled back the sheet, his chest skin was white. His face had been charred black.

''Industrialized countries don't have burn centers to care for these people, but they have the weapons to use in the third world,'' Dr. Rusli lamented.

One of the last groups he cared for was a family of seven. The hair on their heads had been singed off and the features on each of their faces were no longer discernible.

''I never experienced anything like this in Cambodia,'' Dr. Rusli said.

''The difference here is the weapons and their velocity. In Cambodia we didn't have the small fragmentation of shrapnel.''

The shrapnel has phosphorus on it, so it begins burning the minute it imbeds in the body, he explained.

''When we took a big piece of shrapnel out of one man's ankle, we opened the bandages on the operating table and smoke came out. The man was wounded 10 hours before. The leg had burned for 10 hours.''

''Usually war is on the battlefield,'' Dr. Rusli said. ''Seventy percent of my patients are civilians. Women and children aren't in the army.''