Menachem Begin, Ariel Sharon and Rafael Eitan appear to have accomplished what none of Israel's Arab enemies could do--inflict upon the Israeli Defense Forces (IDF) a grievous wound from which it may take years to recover.

The Army is a near sacred institution in this country. From the moment of its birth, Israel has lived in a state of real or semi-siege. The IDF was its shield against its hostile neighbors. Three generations of Israeli youths have served in it, and over the years the country has swelled with pride not only because of its military prowess, but because of its generally exemplary conduct amid the brutal realities of the Middle East.

But in the past week, the credibility of the Army and of the Begin government have been torn by the revelations of Israel's role in the massacre of Palestinian refugees in West Beirut.

No Israeli soldier has been reported to have taken part in the slaughter. Moreover, there are numerous reported instances of Israeli soldiers and officers stationed near the Shatila and Sabra camps sending alarmed reports of the massacre back to their command centers starting shortly after the killing began.

But, as is now clear, at the top echelons of the government and the military, where the decision to send the Christian Phalangist militia into the refugee centers had been made, nothing was done until the militiamen had been given 36 hours to accomplish their grisly task.

There are daily new revelations of what the IDF knew about what was going on inside the camps, when, and what it did about it. Each new bit of information seems to contradict the last official statement, requiring a new statement and new admissions to be made. Some high-level military and government officials have resigned--not because they are assuming personal responsibility for the slaughter, but because they object to the government's apparent dissembling that they may, in some cases, unwittingly have been a part of.

When the massacre became public here last weekend, obviously confused military and government spokesmen said the Israeli forces surrounding the refugee areas had not known that armed militiamen had infiltrated into the Palestinian neighborhoods. The spokesman added that the forces moved quickly to halt the slaughter once they learned of it during the day on Friday, Sept. 17. They later amended this to say the massacre was halted sometime Friday night.

At that time, the spokesmen said, Israeli forces approached but did not enter the refugee neighborhoods, using loudspeakers to order the militiamen out and in some cases exchanging fire with "extremist" Phalangist units.

All that was known at the top levels of the government and military on Friday, the spokesmen said, were a series of vague and often conflicting rumors and reports that "something is wrong" in the West Beirut refugee centers.

Against these earlier versions, it is now possible to reconstruct when senior Israeli officials made the critical decisions between Wednesday, Sept. 15, and Saturday, Sept. 18. Most of the information has been publicly acknowledged by Defense Minister Sharon in a speech to the Israeli Knesset (parliament) or has been widely reported in the Israeli press without denial by government and military officials.

Wednesday, Sept. 15: The decision to send Israeli troops into West Beirut, to prevent what the government later said was anticipated bloodshed following the assassination of president-elect Bashir Gemayel the day before, was made at 12:30 a.m. by Prime Minister Begin and Sharon, in consultation with Foreign Minister Yitzhak Shamir.

In a television interview last night, however, Sharon acknowledged for the first time that this reason provided by the military command was only a "smoke screen" to hide Israel's real intention -- the destruction of the remaining Palestinian guerrillas thought still to be in the city.

Even before the Israeli Army began to move on the ground, its chief of staff, Gen. Eitan, and its northern commander, Gen. Amir Drori, had begun to make the first preparations to send the Phalangist militia into the refugee centers. At 3:30 a.m., they met with the Phalangist staff in Beirut. At this meeting, according to Sharon, "there was discussion in principle of their entry into the camps."

At 5 a.m. on Wednesday, the Israeli Army began moving into West Beirut with explicit orders to stay out of the refugee areas. That afternoon, Israeli officers received "an absolute negative answer" to their request to the Lebanese Army that it take on the task of clearing the guerrillas from the refugee centers, according to Sharon.

Wednesday night, Drori met with the Phalangist commander and with Col. Michel Qun of the Lebanese Army. Again, according to Sharon, Drori urged that the Lebanese Army enter the refugee neighborhoods. Again, the answer was no.

Why ranking Israeli officers were urging this on the Lebanese Army when they had already approached the Phalangists about cleaning out the camps has not been explained.

Thursday, Sept. 16: At 11:20 a.m. the military command in Tel Aviv and Jerusalem announced that "the IDF is in control of all key points in Beirut. Refugee camps harboring terrorist concentrations remained encircled and closed."

On Thursday afternoon, Drori met again with the Phalangist commander in Beirut. Later the same day, the Phalangist commander met with the Israeli Army's divisional commander in Beirut "to coordinate the entrance of the Phalange units to the Shatila camp," Sharon said.

Earlier versions of events provided by the military command maintained that the Israeli Army had not actually encircled the refugee areas but held positions only on the north, south and west. The militiamen entered from the unguarded east, military spokesmen said.

But, as Sharon acknowledged in his Knesset speech, at these meetings Thursday afternoon "the conclusion was that a military force would enter the Shatila camp from the south and west, comb out and mop up terrorists." At these meetings, Sharon emphasized, the Christian militia leaders were told that "the action was to be against terrorists and that the civilian population should not be harmed, especially women, children and old people."

Thursday evening, the Phalange units began entering the refugee centers under the illumination provided by flares fired from Israeli mortars and dropped from Israeli planes. According to a report by Michael Elkins of the British Broadcasting Corp., Phalangist commanders were in radio contact with Israeli liaison officers outside the camps "and called in a request for flares."

A short time later, Israeli soldiers on the ground began to encounter hysterical Palestinian women running from the refugee neighborhoods and telling of a massacre going on inside. These accounts were relayed to officers and presumably transmitted along the chain of command.

At 11 p.m., the Israeli Army division command in Beirut received a report from the Phalangist commander in Shatila. "Until now 300 civilians and terrorists have been killed," it said. The report was relayed to IDF headquarters in Tel Aviv.

Meanwhile, in Jerusalem, the Israeli Cabinet met late into the night to consider a renewed demand by the United States that it withdraw its forces from West Beirut. There, Sharon and Eitan presented the plan to send the Christian militia units into the camps to root out the guerrillas.

The consensus among the ministers, according to Israeli press accounts, was that it was about time that Lebanese Christian forces shouldered their share of the burden against the Palestinians. There was no dissent as the Cabinet authorized a military operation that almost certainly was already under way.

Friday, Sept. 17: In the morning, Zeev Schiff, the military correspondent of the independent newspaper Haaretz, learned of the massacre from Israeli Army officers. He relayed the information to Communications Minister Mordechai Zippori, who in turn called Foreign Minister Shamir with the disturbing news.

In a television interview, Sharon acknowledged that the reason provided by the military command was only a "smoke screen" to hide Israel's real intention -- the destruction of the remaining Palestinian guerrillas thought still to be in the city.

Shamir asked Foreign Ministry personnel about Zippori's information and was told they knew nothing about it. At about noon, the foreign minister and Sharon met in Jerusalem with U.S. envoy Morris Draper and urged him to pressure the Lebanese government into sending its Army into the refugee centers, Israeli officials said.

They apparently did not mention to Draper what both of them then knew -- that the Phalangist units had been in the refugee neighborhoods for more than 12 hours. No one has explained why Eitan and Drori agreed to allow the militiamen another 15 hours to complete their rampage, given the eyewitness reports from soldiers, the report of civilians being killed that was transmitted by the Phalangist commander to Israeli divisional headquarters and the suspicions raised by the Israeli divisional commander.

In Beirut at 11 a.m. on Friday, according to Sharon's account to the Knesset, Drori met with his divisional commander, who "raised suspicions regarding the Phalange mode of operations." Drori contacted the Phalangist liaison officer to the Israeli forces and ordered an immediate halt to the Christian militia's operation.

At 4:30 p.m., Eitan and Drori met with the Phalangist staff. At this meeting, according to Sharon, "it was concluded that the Phalange would all leave the refugee camp on Saturday in the morning. It was also concluded that an additional force would not enter the camps. In this meeting as well, the events inside Shatila camp were not known."

No one yet has explained why Eitan and Drori agreed to allow the militiamen another 15 hours or so to complete their rampage, given the eyewitness reports from soldiers Thursday night, the report of civilians being killed that was transmitted by the Phalangist commander to Israeli divisional headquarters late that night and the suspicions raised Friday morning by the Israeli divisional commander.

Friday night, according to a report on Israeli television yesterday, Sharon was awakened by a telephone call from Ron Ben Yishai, the military correspondent for Israeli television, who told him about the massacre. Ben Yishai said Sharon replied, "Happy new year."

On the same television program, Sharon denied not having taken action after the phone call but said that "local commanders" in Beirut assured him that the military operation was over.

Saturday, Sept. 18: The Phalange militiamen left the refugee centers in the morning as they had agreed to the day before. According to eyewitness accounts from Beirut, the bulk of the killing took place between nightfall on Friday and dawn on Saturday, the first day of the Jewish new year.