In Israeli Cabinet minister testified today that he told Foreign Minister Yitzhak Shamir of a reported "massacre" taking place in the Palestinian refugee camps of West Beirut more than 18 hours before the slaughter ended.

Communications Minister Mordechai Zippori, appearing before the judicial board of inquiry investigating the massacre, said he received the information on Sept. 17 from Zeev Schiff, the military correspondent of the independent newspaper Haaretz, who said he had been told of the massacre by Israeli Army officers.

Zippori said he sought immediately to relay the information to the Army's director of military intelligence and the head of Israel's General Security Services. But he said both men were then en route to Jerusalem from Tel Aviv for a meeting in Shamir's office and so he called the foreign minister.

"I told him," Zippori said, " 'Yitzhak, reports have reached me that the Phalangists are massacring. I suggest, I request . . . that you check the matter out via your channels, or with the men that will be with you soon. I know that they are coming to you.' "

He said Shamir replied, "I heard you."

Zippori's testimony was among the most damaging the inquiry board has heard in public about the extent of information concerning the massacre that reached the highest levels of the Israeli government while the killing was still going on. He is the first witness to refer in public to reports of a "massacre." All the others have maintained that their information at the time consisted of vague and often conflicting "rumors" about possible "irregular behavior" or unusually high civilian casualties in the refugee camps.

Zippori said he spoke with Shamir late on the morning of Sept. 17. That afternoon in Beirut, the Israeli Army's chief of staff, Lt. Gen. Rafael Eitan, gave Lebanese Christian Phalangist commanders permission to keep their units inside the Sabra and Shatila refugee camps until 5 a.m. Sept. 18. The last of the militiamen, who had entered the camps on Sept. 16, did not leave until a few hours after the 5 a.m. deadline.

Schiff, one of the most highly respected journalists in Israel, reported his conversation with Zippori shortly after the massacre. He did not identify the minister by name in the article, but this soon became known.

At the time, a spokesman for the Foreign Ministry acknowledged that Shamir had received a phone call from Zippori on Sept. 17 concerning "shootings" involving civilians in the Palestinian neighborhoods. The spokesman said Shamir asked Foreign Ministry personnel about the report and, told that they knew nothing about it, did not pursue the matter.

A short time after hearing from Zippori, Shamir attended a meeting in his office with Defense Minister Ariel Sharon, U.S. envoy Morris Draper and others, including the chiefs of military intelligence and General Security Services. According to earlier testimony before the commission, the subject of the Phalangist militia units' presence in the refugee camps was not mentioned during the meeting.

Shamir has not yet been called to testify before the inquiry board. Sharon testified that the first he knew of widespread civilian deaths in the camps was at 9 p.m. Sept. 17, while Prime Minister Menachem Begin told the panel he knew nothing of the events in West Beirut until late the next afternoon.

Zippori said he met Schiff, whom he described as an old friend, at 11 a.m. on Sept. 17. "The first thing, as he entered, he said to me, 'Motke, I have reports that the Phalangists are massacring in the camps,' " Zippori said, adding that Schiff "told me that officers had told him, straight."

Under questioning, Zippori said Schiff did not specifically mention the killing of women and children or provide any numbers of civilian deaths. "The moment he had told me that there is a slaughter there, and that Phalangists are running wild, I did not wait for more details," he said.

After relaying the information to Shamir, Zippori said, he took no further action because he trusted the foreign minister. "And besides, since perhaps I am considered a snoop, I stopped nosing around," he said.

Zippori, a former deputy defense minister and an internal political rival of Sharon, also took issue with the assertions of Sharon and Begin that the defense minister was authorized to order the Phlanangist militia units into the refugee camps on his own.

It is true, Zippori said, that on June 15, the second week of the war in Lebanon, the Israeli Cabinet secretly agreed to use Phalangist forces to fight in West Beirut as a way to hold down Israeli casualties. Moreover, throughout the war there were complaints about why so little fighting was being done by the Phalangist units, he said.

But Zippori said the June 15 Cabinet decision was "definitely not" sufficient authorization for Sharon unilaterally to order the Phalangist units into Sabra and Shatila.

The Israeli Cabinet was informed of Sharon's decision about about two hours after the Christian militiamen entered the camps, and, according to previous testimony, none of the ministers suggested that it be reversed. During that meeting, Deputy Prime Minister David Levy warned about the possible consequences of using the Phalangist units, but Zippori said today he did not hear Levy's remarks because he was in the bathroom.

The inquiry board granted Zippori's request to discuss the June 15 and Sept. 16 Cabinet meetings in more detail in a closed session.