The Israeli Cabinet, under intense domestic and international pressure, today authorized the creation of a state judicial board of inquiry to investigate Israel's role in the massacre of Palestinians at two refugee camps in West Beirut.

The decision, which was a victory for opponents of Prime Minister Menachem Begin, followed more than a week of turmoil in Israel and came nine days after the government had declared that Israel bore no responsibility for the mass killings.

Today the Cabinet unanimously authorized the investigation into all aspects of the incident, including decisions and actions of Israeli political and military leaders from Begin on down.

In a statement read to reporters by Cabinet Secretary Dan Meridor, the Cabinet said it took the step at Begin's suggestion "in order to put an end to the false libels to the effect that the Israeli government has something to hide in this matter, or that it would like to avoid its full clarification."

Begin had fiercely resisted any kind of investigation, contending that this would amount to an admission of guilt by Israel.

Deputy Prime Minister David Levy said the Cabinet's authorization to the inquiry board did not exempt any topic from examination. "Everything is open for investigation," he said.

According to Prof. Claude Klein of the Hebrew University law school, the new board of inquiry will be the sixth in Israel's history. Usually composed of three members, the inquiry board must be headed by a judge or retired judge and is appointed by the chief justice of the Supreme Court, who may name himself chairman. It is more powerful than other investigative panels because it has subpoena power to summon witnesses and documents, and because its members enjoy immunity from lawsuits in their official capacity.

Begin had earlier proposed that the chief justice of the Supreme Court head a lower-level probe, but the justice refused because he had before him independent requests for a full-fledged board of inquiry.

The political effect of the massacre was indicated today by a decision to call off a progovernment rally scheduled for Saturday in Tel Aviv.

The rally had been planned to counter the huge demonstration staged in Tel Aviv last week by the political opposition. Officials said the progovernment rally was being cancelled to prevent further polarization of Israeli society, but it also seemed to be a tacit admission of the government's weakened position.

The main opposition Labor Party later announced that it was calling off a scheduled debate in the Knesset, or parliament, Thursday as a gesture in response to the creation of the inquiry board.

Many of the circumstances surrounding the Israeli Army's coordination and assistance to the Christian Phalangist units that rampaged through the Shatila and Sabra refugee camps in West Beirut have been publicly acknowledged by Defense Minister Ariel Sharon and others. The officials have maintained, in their own defense, that when they sent the militiamen into the camps to root out Palestinian guerrillas they never dreamed that a massacre of hundreds of men, women and children would result.

That assertion, however, came under more questioning today as a result of a report in the independent newspaper Haaretz. The newspaper's military correspondent, Zeev Schiff, reported that the massacre was not a spontaneous act of rage by Phalangist militiamen seeking to avenge the assassination of their leader, Lebanese president-elect Bashir Gemayel, but was "a premeditated action designed to frighten the Palestinians into mass flight from Beirut and Lebanon."

Citing "official sources," Schiff said the Phalangists had discussed just such a strategy weeks before the massacre. He also reported that the commander of the militia units that entered the Shatila neighborhood, Ali Haika, had been forced to leave southern Lebanon by the Israeli Army after complaints about his activities from Israel's other Lebanese Christian ally who operates in the south, former Lebanese major Saad Haddad.

In addition to the circumstances that led to the massacre, the inquiry board is expected to investigate when Israeli officials learned of the mass killings and whether they could have acted to halt them. A senior official said today that Begin first learned of the massacre from a news report by the British Broadcasting Corp. at 5 p.m. on Sept. 18, well after the Phalangist units had left the refugee centers.

Other officials, including Sharon, insist they heard only vague "rumors" about the slaughter, although the Israeli Army division command in Beirut reportedly received an account of the killing of civilians from Phalangist commanders on the first night of the massacre, Sept. 16.

Establishment of the board of inquiry did not still the chorus of demands for Sharon's resignation. The defense minister reportedly is under heavy fire even within the government as a result of the massacre and some of his public comments since then.

Sharon, speaking at a memorial ceremony for soldiers killed in the 1973 war, said that "contrary to past cases, I recognize and believe in the concept of ministerial responsibility," The Associated Press reported. This was an oblique reference to his late predecessor Moshe Dayan, who refused to resign after an investigation of the 1973 war exposed shortcomings in the Army.

The probe into the 1973 war was the best known of the previous boards of inquiry and its findings contributed to the downfall of the Labor Party government in the 1977 elections.

There also appeared to be considerable political maneuvering by factions within Begin's government coalition seeking to distance themselves from the prime minister and Sharon, and speculation that Ezer Weizman, forced out as defense minister by Begin, who replaced him with Sharon, may be called on to reenter active political life.

Yitzhak Berman, who resigned as energy minister when the government first refused to investigate the massacre, said he will not reconsider his resignation. But Gen. Amram Mitzna, who resigned as commander of the Army's command and staff college, agreed today to return to his post. Mitzna had been threatened with discharge from the Army if he did not retract the resignation.

West Bank administrator Menachem Milson, who also resigned to protest the massacre, was replaced by Col. Yigal Carmon, a Defense Ministry adviser on Arab affairs, who was to serve until a new civilian administrator could be named.

Earlier today, Foreign Minister Yitzhak Shamir left for the United States, where he is to spend the next month attempting to bolster support in the American Jewish community for the beleaguered Begin government.

Shamir will first attend the opening of the U.N. General Assembly session in New York before taking off on a cross-country tour to the West Coast and back, ending with meetings with Reagan administration officials in Washington Oct. 14 and 15.

In a statement at Ben Gurion International Airport near Tel Aviv before he left, Shamir appealed for unity in Israel against what he called the "baseless accusations that are being spread throughout the world against us so as to vilify and outlaw us."