Defense Minister Ariel Sharon said today that he had anticipated civilian casualties when he authorized Christian Phalangist militias to enter the Beirut refugee camps of Sabra and Shatila, but not the 700 to 800 deaths he said Israeli intelligence officials estimate occurred during last month's Phalangist rampage.

Testifying before the state judicial board of inquiry investigating Israel's role in the massacre, Sharon said the Israeli government decided earlier in the war in Lebanon to use Christian Phalangist militiamen to fight Palestinian guerrillas in West Beirut. But he said government leaders never dreamed that this would lead to the massacre of civilians months later in the refugee camps.

Sharon said the Israeli Cabinet made the decision June 15, during the second week of the war, and saw it as a way to hold down Israeli casualties. The defense minister, flanked by two senior Army officers, testified for 2 1/2 hours in the first open session the inquiry board has held since it began its investigation last week.

"I want today, in my name and on behalf of the entire defense establishment, to say that no one foresaw -- nor could have foreseen -- the atrocities committed in the neighborhoods of Sabra and Shatila," Sharon said, according to a summary and translation of his testimony released by the government press office. Sharon testified in Hebrew.

Sharon, dressed in a gray suit and tie and more subdued than usual, provided a few more details to what is already known about the events in the refugee camps between Wednesday, Sept. 15, and Saturday, Sept. 18. There was immediate speculation after his public appearance -- which was followed later today by a three-hour closed-door appearance before the commission -- that his testimony would widen the rift between him and senior military officers, particularly Chief of Staff Gen. Rafael Eitan.

Sharon said the first news he had of widespread civilian casualties in the refugee camps came in a telephone call to him from Eitan about 9 p.m. Sept. 17, about 24 hours after the Phalangist units had entered the refugee neighborhoods.

He said Eitan told him the civilian casualties inflicted by the militiamen already exceeded Israeli expectations.

"They went too far," the defense minister quoted Eitan as saying.

Sharon said that in the same conversation Eitan assured him that at a meeting with Phalangist commanders earlier that day the chief of staff and Israeli northern commander Gen. Amir Drori had ordered the militia units to cease their operations in the camps, had prevented them from bringing more soldiers into the area and ordered them to remove all of their troops from the Palestinian neighborhoods by 5 a.m. the next day.

Sharon said he considered this a "reasonable" amount of time to allow the Phalangist units to extract themselves from the teeming refugee neighborhoods.

As a result of these assurances, Sharon went on, he took no further steps despite additional reports of the massacre that reached him later that night.

According to eyewitness accounts from Beirut, most of the killing took place that Friday night, after Eitan and Drori had ordered a halt to the operation. The implication of Sharon's testimony was that the main responsibility lay with Eitan, who had assured him that the killings had been halted.

Sharon also suggested in his testimony that Prime Minister Menachem Begin may have known something of the events in West Beirut hours earlier than he has acknowledged. Sharon said that on Saturday morning, Sept. 18, Eitan said Begin had called him inquiring about reports he had heard concerning the Gaza Hospital, which is in Sabra.

There was no elaboration on this point. Begin has insisted that the first news he had of the massacre was from a British Broadcasting Corp. newscast at 5 p.m. Sept. 18.

Throughout his testimony, Sharon insisted that he and others never considered the possibility of a massacre by the Phalangist units. On Sept. 16, the night the militiamen entered the camps, he said he met with U.S. envoy Morris Draper, urging that the Lebanese Army be dispatched to the Palestinian neighborhoods, not because he feared a massacre but because he doubted the Phalangist units alone could defeat the Palestinian guerrillas Israel says were in the camps.

"No one even imagined or spoke of or worried about this [a massacre], and I begin with myself," he said.

This assertion is in conflict with an authoritative account provided earlier to The Washington Post that while arguing for the use of regular Lebanese Army troops Sharon predicted the possibility of a Phalangist massacre. There was no reference to this account today.

Sharon's disclosure of the Cabinet's June 15 authorization for the use of Phalangist troops confirmed a widespread impression here that the Israelis hoped the final assault on the Palestine Liberation Organization strongholds in West Beirut would be taken on by their Christian allies, holding down Israeli casualties.

However, Phalangist units refused to enter West Beirut until after the evacuation of thousands of heavily armed PLO guerrillas and Syrian Army troops.

Sharon's testimony, before a three-member commission headed by Supreme Court Justice Aharon Barak, took place in a heavily guarded lecture hall on the West Jerusalem campus of Hebrew University.

Sharon said he considered the Phalangist units to be made up of disciplined soldiers but conceded that their conduct in battle was often different from that of the Israelis. He said that earlier in the war Israeli forces had prevented Phalangist units from destroying the Miyah refugee camp near Sidon.

He denied a report that during a Cabinet meeting on Sept. 16 Deputy Prime Minister David Levy had warned of a possible massacre. Sharon said Levy only cautioned that Israel would be blamed for anything that went wrong while its troops occupied West Beirut. "Nobody objected to the operation," he said.

Sharon also said that he is convinced that units commanded by Israel's other Christian ally, former Lebanese Army major Saad Haddad, played no role in the massacre.

The commission is expected to continue its investigation for several more weeks, possibly hearing later from Begin. A spokesman said tonight it is not known whether Sharon will be recalled for additional testimony.