Lebanese Christian militiamen moved into Palestinian refugee camps two weeks ago in accordance with an operational plan designed and approved by the highest military echelons of Bashir Gemayel's Lebanese Forces militia, including Gemayel himself before his assassination on Sept. 14.

Nothing in the plan called for the wanton slaughter that occurred in the Shatila and Sabra camps once the militiamen had moved in. But, a variety of well-informed sources now say, that plan did call for arrests, interrogations and physical destruction of housing as part of a broader effort to spread terror among Lebanon's estimated 500,000 Palestinian refugees to encourage them to flee the country.

These sources have established that the operation in the camp was carried out by about 500 elite troops of the Lebanese Forces, including members of the militia's special commando unit, its military police and the intelligence security units. Sources in the Lebanese Christian community said that the operation had been under the command of 28-year-old Elie Hobeika, one of the closest associates of Gemayel, who was leader of the Lebanese Forces and president-elect of Lebanon at the time of his death.

Hobeika, the chief of intelligence for the militia, was also the Lebanese Forces' chief contact with Mossad, the Israeli secret service, as well as with the U.S. Central Intelligence Agency, Lebanese sources said.

What happened to turn the Gemayel plan from a sweep through the camps in search of armed Palestinians and men of military age into a murderous rampage that left at least 597 unarmed civilians dead still is not clear. Grief over his assassination may have been an emotional factor. But it is also true that massacres have been committed against civilians on both sides during the seven years of warfare in Lebanon, with Palestinians most frequently having been the victims.

There is also no direct evidence that the newly installed president, Amin Gemayal, 40, Bashir's elder brother, knew of the plan beforehand, or was aware that the Lebanese Forces' General Staff had been involved in executing it. But there is growing concern within the Christian community that he may be tainted by a Phalangist effort to shut off questioning about the massacres and to cover up the responsibility of the commanders of the units that have now been identified as having taken part in the slaughter.

These conclusions emerge from a week-long inquiry that included extensive interviews with Lebanese politicians, officials of Bashir Gemayel's Phalange Party, staff officers in his militia command, Lebanese government officials, members of the Lebanese Army and police, and Western diplomats who have been following events in Lebanon with growing concern.

The difficulties involved in such an inquiry were underscored by repeated warnings delivered to this correspondent and to Colin Campbell of The New York Times, who was pursuing a parallel investigation. Both of us left Lebanon today after word was passed to us through diplomatic channels that our lives might be in danger because of our line of questioning. Sources interviewed for this story, citing the same risks to them, all requested anonymity.

Phalange officials, when asked for a formal comment on the accusations being made against the senior commanders of the militia, declined, saying that an inquiry was being conducted. The officer in charge of the investigation into the massacres is Elie Hobeika, these officials said.

There has been nothing here that compares with the public uproar in Israel demanding an official full-scale inquiry into Israel's role in letting the militia units into the camp, nor anything like the public discussion by Defense Minister Ariel Sharon of the background leading up to the tragedy that occurred Sept. 16-18.

"No one wants the real story to come out because it could be dynamite for this poor country," said a senior Western diplomat. "The president Amin Gemayel knows where any such inquiry leads. It would be both dangerous physically to him and politically explosive."

"The president does not command here," said a Christian lawyer. "It is the Lebanese Forces who command now, and they have every intention of continuing to do so."

The most powerful figure in the Lebanese Forces now appears not to be the commander in chief, Fuad Ephraim, who was given the job earlier this month by his mentor, Bashir, but Hobeika, a man described by one senior Western diplomat as "very tough, absolutely ruthless, a man who has been a fighter since he was 14."

The other most important figures in the Lebanese Forces command are the heads of units that witnesses say were identified as being in or around Shatila and Sabra at the time of the massacres. They include Dib Anastas, the head of the military police, and Joseph Edde, the commander of the militia's special black-bereted commandos and of all Lebanese Forces' units south of Beirut.

There was also at least one contingent of militiamen from the town of Damour, south of Beirut, whose men had sworn vengeance against all Palestinians because of the sacking of Damour during the 1975-76 Lebanese civil war.

Anastas played a prominent role during the civil war siege by the Lebanese Forces of the Palestinian refugee camp of Tal Zataar, where several thousand civilians died in 1976.

Lebanese sources who knew of the original plan to send the militia into the camps say the idea was discussed and approved sometime between Bashir Gemayel's election to the presidency Aug. 23 and his death in a bomb explosion at a local headquarters of his Phalange party in East Beirut Sept. 14.

Gemayel's plan, according to these authoritative sources, envisoned the disarming of any armed Palestinians left in the camps after last month's U.S.-negotiated evacuation of the Palestine Liberation Organization, widespread arrests and interrogations of refugees and the destruction of some "squatter" housing. The purpose, in part, these sources said, was to make it clear to the Palestinians that they should all leave Lebanon.

"It was not a question of killing women and children and old men as happened at Shatila," a highly placed Lebanese source insisted, "but to go into the camps to eliminate all the remaining PLO terrorists that Bashir, and Israel, believed had stayed behind after last month's evacuation."

Expelling the Palestinians from Lebanon has long been an item of priority in the platform of the ultrarightist Phalange Party founded by 77-year-old Pierre Gemayel, the patriarch of one of Lebanon's dominant Christian Maronite political clans.

Whether the Israeli government was aware of this plan either as it was being worked up or in the wake of the assassination of Bashir Gemayel is not clear. What has been established is that at 3:30 p.m. on Sept. 15, Israeli chief of staff Rafael Eitan and Gen. Amir Drori, the commander of Israel's occupying army in Lebanon, went to the Lebanese Forces' whitewashed headquarters building near the port of Beirut and met with the militia's general staff, which is chaired normally by the militia's commander in chief, Fuad Ephraim.

According to Sharon's statement on the events leading up to the operation in the camps, the issue of the militia's entry into the camps was mentioned "in principle" at that meeting, which also apparently included the commanders of the units that would later take part in the operation.

At a subsequent meeting with Ephraim and Col. Michel Oun, the pro-Phalange Lebanese Army commander in West Beirut, Drori urged that the religiously divided and weak Lebanese Army be ordered into the camps to collect all weapons held by Palestinians. That request was turned down by Prime Minister Shafiq Wazzan, who apparently was not prepared to take the responsibility for leaving the camps unprotected.

Sometime that night the Lebanese Forces' general staff, acting in the absence of its 13-man political "war council," met again and decided to order some 1,500 of their special troops to assemble during the course of the following day at Beirut International Airport south of the capital, in an area tightly controlled by the Israeli Army -- which until today used the airport runways as its own military air field.

As can best be pieced together from reports of the various uniforms seen inside the Shatila camp by massacre survivors, unit identifications spotted by eyewitnesses along the militia route to the airport, as well as authoritative leaks emanating from Israel, these units consisted of: Anastas' military police, Edde's black beret commandos, Hobeika's own special security units, and the Damour unit.

There were also a handful of men spotted who appeared to belong to the militia of renegade Lebanese Army major Saad Haddad, Israel's surrogate in a buffer zone north of its borders in south Lebanon.

Though the official Phalangist denials maintain that no "regular" Lebanese Forces units were sent to Shatila Thursday, Sept. 16, a senior man on the general staff has privately confirmed that from 9 a.m. to 3 p.m. that day 1,500 men from his militia did in fact assemble at the airport.

This admission corroborates eyewitness accounts of troop movements Thursday, including that of 11 antiquated Sherman tanks, toward the airport. The troop movements were both from East Beirut north of the airport and from the south along the coastal highway that leads to the capital from Damour and the big Lebanese Forces encampment above the campus of the International College at Mishraf.

Not all units assembled at the airport that Thursday went into the camp. Which ones did is still not totally clear, though helmets with the military police's distinctive red bands were spotted by survivors and foreign hospital workers as were black berets usually worn by the elite commandos.

Road signs guiding the militiamen from the airport to the outskirts of the camp also tend to confirm the military police's presence since the signs, painted on walls and buildings along the route, bore the Lebanese Forces emblem of a triangle within a circle, the letters "MP" and arrows pointing out the route to the camp.

From all reports it seems probable that the militia force in the camp was no bigger than 500 men, maybe even much less. The rest apparently stayed at the airport under Israeli protection as a reserve force in case they were needed.

The slaughter of hundreds of Palestinian men, women and children began that Thursday night, continued through Friday, and did not end until early Saturday morning, Sept. 18, when the militiamen withdrew. They left behind them mass graves, bodies littering homes and alleyways, and a major scandal that has rocked the Israeli government and cast a shadow over the future of President Amin Gemayel, who was elected by Parliament and inaugurated in a span of two days last week.

The new president has made numerous visits to the Lebanese Forces headquarters to closet himself with its Command Council and General Staff since his election last week. These meetings have been held despite the fact the new president publicly exonerated the militia and the Phalange Party of having any knowledge of the Shatila massacres, a statement that has reinforced the general suspicion that despite the formation of an investigation commission under an Army prosecutor-general that stonewalling is going on.

As the emerging major figure in the Lebanese Forces, Hobeika owes his position to the president's late brother. Hobeika was deeply devoted to Bashir Gemayel since they were a part of a young group of Christian militants who were known before the civil war of 1975-76 as the saqr, or rock, group. When, during the civil war, Bashir Gemayel arranged for Israel to give his embattled Christians military aid, it was Hobeika who was one of the first of a group of young fighters loyal to the commander who was sent to Israel for training under Mossad and the Israeli Army.

Diplomatic sources said that many of the key operational contacts were conducted by Hobeika in the name of Gemayel.