JERUSALEM, SEPT. 5 -- Israeli warplanes bombed Palestinian targets in southern Lebanon today, and reports from Lebanon said at least 40 persons were killed and 60 wounded, making it the bloodiest air raid since the 1982 Israeli invasion.

The raid on Palestinian bases outside the southern port city of Sidon was the 22nd Israeli air attack in Lebanon this year but the first in memory on the Jewish Sabbath.

A Lebanese police spokesman, quoted by news agencies, said most of the casualties were Palestinian guerrillas caught by surprise when the jets launched a second raid while the guerrillas were evacuating victims of the first attack. But Reuter quoted police and hospital officials as saying that at least four women and four children were among the dead.

Witnesses at the scene told Reuter that the 10-minute, midmorning blitz by three waves of warplanes sent black smoke billowing into the sky on the outskirts of Ain Helweh refugee camp outside Sidon, about 25 miles south of Beirut.

Explosions continued to be heard minutes after the warplanes had swept back south to Israel, indicating that some of the bombs might have been armed with delayed action fuses, the wire service reported.

An Israeli military spokesman asserted the targets were used as headquarters for Palestinian "terrorist organizations that planned to embark on attacks against Israel in the near future."

A spokesman said Israel could not confirm the casualty reports but added, "It is unusual for an attack to take place on Shabbat {the Sabbath}, and that is probably the reason for the large number of casualties."

He gave no reason for the timing of the attack and said it was not in retaliation for any specific Palestinian attack on Israel.

But last night Israel announced the capture of a Palestinian squad that it said was responsible for a number of recent bomb attacks in Israel.

The cell, which was said to belong to Fatah, the mainstream faction of the Palestine Liberation Organization headed by Yasser Arafat, had carried out attacks on civilian buses in Israel, according to reports here.

The Israeli announcement said the members of the squad were arrested after one member was injured while trying to place a bomb on a Tel Aviv bus a week ago. The number and names of those detained were not released.

In this morning's attack, at least four Israeli jet fighters carried out three dive-bombing sorties against five Palestinian guerrilla bases on the eastern and southern edges of Sidon, according to the Lebanese police spokesman quoted by The Associated Press.

Three of the targets belonged to Fatah, said the spokesman. One base belonged to the Marxist Popular Front for the Liberation of Palestine, and the other was an office for the terrorist organization Abu Nidal, the spokesman said.