After 17,703 pages of evidence, testimony by 49 witnesses and interviews with 152 eyewitnesses, Israel today completed its 3 1/2-month investigation into the September massacre of hundreds of Palestinian refugees in West Beirut.

The final act in the investigation was played out in a closed lecture hall on the campus of Hebrew University where lawyers for six senior Israeli officials made closing oral arguments before the three-member judicial board of inquiry that is conducting the investigation.

The panel will now begin drafting its final report on Israeli responsibility for the massacre, which was perpetrated in the Sabra and Shatila refugee camps by armed units of Israel's Lebanese Christian allies. Israelis have not been accused of taking part in the massacre, but the Christian Phalangist militia units that did had entered the refugee camps with the coordination and assistance of the nearby Israeli Army group that occupied West Beirut.

The commission has not indicated when it will complete its report, but it was widely expected that the findings will be made public sometime next month.

In November, the investigative commission warned nine senior officials, including Prime Minister Menachem Begin, Defense Minister Ariel Sharon and Foreign Minister Yitzhak Shamir, that they are liable to be harmed by its findings. It offered them a chance to present new evidence and otherwise defend themselves in a process that was climaxed by today's more than two hours of oral arguments.

The six officials whose lawyers pleaded their cases today were Sharon; Lt. Gen. Rafael Eitan, the Army chief of staff; Maj. Gen. Amir Drori, the Army's northern commander; Brig. Gen. Amos Yaron, commander of all Israeli forces in Beirut; the head of Israel's intelligence service, the Mossad, who under Israeli law cannot be named in public, and Avi Dudai, Sharon's personal assistant.

Begin, Shamir and Maj. Gen. Yehoshua Saguy, the chief of military intelligence, did not have closing arguments presented in their behalf to the board.

The inquiry board's final report, particularly if it corresponds to the warnings regarding possible findings of negligence of duty by the officials, is expected to set off a major political debate and could lead to elections in Israel later this year.