Lebanese gunmen belonging to right-wing Christian militia units killed hundreds of men, women and children in two undefended Palestinian refugee camps overnight, according to accounts by survivors given to correspondents who counted scores of corpses lying in the streets of the camps today.

The rampage of killing, which extended to babies still in diapers and teen-age girls, started in the war-battered camps of Shatila and Sabra on Friday and continued into the early hours of Saturday, after the militiamen had moved in through an access route from the south that had been controlled by Israeli troops until Thursday night.

Confusion surrounded the precise identity of the killers, who appeared to have systematically machine-gunned everyone within range when they burst into Shatila, on the southern outskirts of Beirut. But a number of survivors identified them as belonging to the units under the control of Saad Haddad, a cashiered Lebanese Army major whose men have been funded and trained by Israel. [In a telephone call to the Reuter news agency bureau in Jerusalem, Haddad denied any involvement and condemned "this savage action."]

Israeli soldiers stationed around the camp and other survivors said the killers also included members of the Phalangist militia, whose leader, Bashir Gemayel, the president-elect of Lebanon, was killed in a still unexplained blast in Beirut on Tuesday. This correspondent saw men wearing the uniforms of both Gemayel's and Haddad's units in Shatila on Friday. The Phalangists, in a radio broadcast, also denied involvement in the killings.

It was impossible to establish a precise death toll immediately. This correspondent counted 46 bodies lying in the open in Shatila before being overcome by nausea. Reporters for United Press International counted more than 100 bodies in a 20-minute walk in the camps, while Associated Press photographers counted about 60.

But bodies were strewn across acres of wreckage in the camps, which had housed more than 10,000 persons before Israel launched its June 6 invasion of Lebanon. Houses had been dynamited and bulldozed into rubble, often with their inhabitants still inside. Hundreds and perhaps thousands more were reported as missing or having been seen being taken away from the camps by the militiamen.

The PLO's representative at the United Nations, Zehdi Terzi, charged that "1,500 helpless civilians . . .were butchered in cold blood" at Shatila.

The International Committee of the Red Cross said in a statement issued at its headquarters in Geneva Saturday that its delegates saw hundreds of bodies lying in the streets, Reuter reported.

"Injured people were killed in their hospital beds, others were kidnaped, as well as doctors," the statement added.

Survivors said the gunmen had moved through the camp beginning after sunset Friday breaking into houses and spraying them with machine-gun fire, as bulldozers rolled behind them, evidently trying to bury many of the corpses under mounds of rubble as quickly as possible. A large pit was excavated near the southern entrance of the camp, and bears the markings of a mass grave.

The killing countinued throughout the night, with the militiamen withdrawing around 8 a.m, witnesses said. When reporters, diplomats and frightened camp residents arrived in midmorning to view the remains of the slaughter, there were no signs of the gunmen or of any Israeli military presence.

Israeli Army units backed by tanks surround the area on three sides, and were in apparent hearing distance of the events in the camp. The Israelis sealed off access to Shatila late in the day, after press accounts of the massacre began to be transmitted. Israeli Army officers with the units around the camps Saturday disclaimed any knowledge of the killings.

Reports of the massacre swept through Beirut and touched off a new wave of terror and recriminations. Former prime minister Saeb Salam, who had negotiated with the Palestine Liberation Organization and U.S. envoy Philip C. Habib this summer to get a PLO evacuation from Beirut, said: "This is what we always feared, and this is what the United States told us would not be allowed to happen. It has, and now the United States, Israel and the Christians must bear responsibility for it."

The negotiations on the PLO withdrawal nearly broke down several times because of Palestinian and Moslem fears that the refugees left behind in the camps would be defenseless against Christian attacks unless a multinational force moved in as the guerrillas were withdrawing and remained to protect the civilians. The Israelis permitted a force of U.S. Marines, Italian and French troops to act as a buffer during the evacuation, but this force left after three weeks of duty.

On Thursday in Rome, PLO leader Yasser Arafat called for a return of the multinational force to Beirut.

Following the evacuation of the Palestinian guerrilla forces, the Israelis moved their troops into the approach area of Shatila and Sabra, around the Bir Hasan area, on Sept. 3. When Gemayel was killed, the Israelis moved their forces completely into West Beirut, asserting that they were doing so to avoid bloodshed. As they moved northward, they shelled and lobbed mortars into the camps, but did not occupy them.

Residents of Shatila and Sabra said they were terrified by the sudden appearance Friday morning of Christian militiamen at the southern gates of Shatila. According to residents just outside the camp area, the militiamen arrived overnight Thursday in trucks, passing through the Israeli Army lines around the camp.

Friday morning, when this correspondent tried to visit the Shatila camp, the Christian militiamen, some wearing uniforms of Gemayel's "Lebanese Forces" militia and others in uniforms of the Gemayel rivals from Haddad's Israeli-backed southern militia, were controlling the southern road into the camp, at a roadblock by the Kuwaiti Embassy just to the southwest of the camp.

On a later visit Friday, at about 6 p.m., the Christian militia roadblocks were not in evidence, although the Israelis were still in their positions on three flanks of the camp. The southern flank, a road that leads from the sea to the Beirut Airport road, was, however, in the hands of the Christians. Turning into the camp off this highway, this correspondent was stopped about 100 yards inside by a group of militiamen, again in the uniforms of both Christian militia groups, and told to skip visiting the camp because things were under control.

But fires already were burning in the camp, and the men talked about meeting resistance as they tried to take control of Shatila. There had been some shooting by terrified Palestinian youths earlier in the day, but they quickly fled as the militiamen advanced into the camp.

A Norwegian diplomat, Gunnar Flaksad, tried to drive to the camp Friday afternoon, and was also turned away, after seeing a front-loading bulldozer leave the camp with what he estimated were at least 20 bodies in the front shovel.

At Gaza Hospital Saturday, 11-year-old Milad Farouk told of the militiamen kicking down the door of his family's modest home and spraying the place with machine-gun fire, killing his father, mother, and younger brother. Milad was wounded by bullets in the arm, leg and hand.

People from the northern part of Shatila and in Sabra heard the screams and shouts in the night, and many of them fled northward, into West Beirut's Hamra commercial district, passing through the Israeli lines of tanks and personnel carriers.

A group of 20 American and European doctors and nurses was arrested by the gunmen at the Gaza Hospital in Sabra camp and marched at gunpoint through the body-littered streets. A Washington woman, Ellen Siegel, a registered nurse associated with the Washington Hospital Center, said the physicians were forced to abandon patients, who had been coming into the hospital since Wednesday as a result of Israeli shelling.

The group was freed when an Israeli colonel walked up to the gunmen "and saw what was happening and told us not to worry," David Gray, one of the physicians, said. Israeli troops then escorted the group to safety in West Beirut.

During their trip through the camp, the medical group saw up to 400 Palestinian civilians being held by the Lebanese gunmen, Siegel said.

Refugee camp survivors Saturday spoke of the killers coming from Haddad's forces, a group created by Israel after their first invasion of southern Lebanon in 1978 to guard a Christian sector of Lebanon just north of their borders. Haddad's forces often have used the uniforms of the Lebanese Forces from East Beirut in an attempt to link them to his own actions.

Israeli Col. Nastali Bahiri, the officer in charge of a group of at least 1,000 Palestinians turned over to the Israeli troops at a nearby sports stadium, said he did not know what had happened in the camp several hundred yards from his position.