Ronald Reagan told a cheering convention of B'nai B'rith here last night that the "weak and confused leadership of Jimmy Carter" had enhanced Soviet power in the Middle East, threatened U.S. security and placed Israel in "grave danger."

In a strongly pro-Israel speech to the Jewish service organization, Reagan was interrupted 30 times by applause as he delivered a stinging indictment of the Carter administration for its Middle Eastern policies and for "undercutting" Israel in the United Nations. He won loud applause when he sharply criticized President Carter for refusing to brand the Palestine Liberation Organization as "terrorist."

Reagan's basic message was that Israel is "a major strategic asset to America."

"While we have since 1948 clung to the argument of a moral imperative to explain our commitment to Israel, no administration has ever deluded itself that Israel was not of permanent strategic importance to America," Reagan said. "That is, until the Carter administration, which has violated this covenant with the past. Can we now have confidence it will honor a covenant with tomorrow?"

Reviewing Carter administration efforts to work out a comprehensive settlement in the Middle East, Reagan said that Israel had "rightly refused" conditions that the PLO be represented at the Geneva Conference and that Israel withdraw to pre-1967 borders.

"Can we believe that Mr. Carter is not still in favor of dealing with the PLO and forcing the terms of a settlement?" Reagan asked rhetorically.

The Carter administration has never made dealing with the PLO its policy. In fact, Carter fired U.N. Ambassador Andrew Young for secretly dealing with the PLO and then misleading other administration officials about it.

Reagan said that the weakness of Carter policies has permitted the Soviet Union to make inroads in the Middle East, which he said is "approaching a flashpoint."

"Our relations with Israel are marked by doubt and distrust," he said. "Israel today is in grave danger, and so is freedom itself."

Reagan said that Carter had failed to fulfill his own call, at the 1976 convention of this Jewish service organization, for a stronger defense and stronger ties with Israel. He credited both Israel Prime Minister Menachem Begin and Egyptian President Anwar Sadat with achieving a bilateral peace, but accused Carter of failing to advance this initiative.

"The quick foreign policy success that Carter had hoped to achieve turned instead into another major foreign policy blunder," Reagan said.

Continuing his review of what Carter had told B'nai B'rith in 1976, Reagan quoted Carter as saying that he was "concerned with the way in which our country, as well as the Soviet Union, Britain and France, have poured arms into certain Arab counties -- five or six times more than Israel receives."

"But it was Mr. Carter who agreed to sell 60 F15 fighters to Saudi Arabia," Reagan said " . . . it was Mr. Carter who agreed to sell 100 main battle tanks to Jordan. It was Mr. Carter who agreed to provide U.S.-licensed turbine engines for Iraqi warships."

Reagan also assailed Carter for insufficiently opposing international terrorism, which the Republican presidential nominee said is increasingly isolating Israel.

"President Carter refuses to brand the PLO as a terrorist organization," Reagan said. "I have no hesitation in doing so. We live in a world in which any band of thugs clever enough to get the word 'liberation' into its name can thereupon murder school children and have its deeds considered glamorous and glorious."

Reagan said the Palestine Liberation Organization has "murdered more Palestinians than Israelis" and "represents no one but the leaders who established it as a means of organizing aggression against Israel."

Reagan said the PLO must do more than renounce agression against Israel to be recognized as legitimate; it also must demonstrate that it represents the Palestinian people.

"If we can be satisfied on both counts, then we will not be dealing with the PLO as we know it but a quite different organization . . . ."

Reagan also blamed Arabs in the touchy issue of Palestinian refugees, saying that problem was created when Arabs left their homeland against the appeal of the newly created Israeli government in 1948. One solution to the refugee problem, Reagan said, "could be assimilation in Jordan, designated by the United Nations as the Arab Palestinian state."

According to some sources in the Reagan camp, the candidate rejected proposals for a less bristling pro-Israel position by those who said this speech could evoke hostile reactions from the Arab world and make it more difficult for Reagan to negotiate with Arab nations as president.

Richard V. Allen, Reagan's principal foreign policy adviser, denied reports of last-minute major revisions in the speech, promised early copies of which were not finally delivered to the press until late afternoon.

"The speech was intended to be balanced," Allen said. It proceeds from a premise of U.S. strategic impotence -- and that's why it sounds pro-Israel."

As in a series of national security speeches last month, Reagan charged that the Carter administration has weakened U.S. military defenses and removed "the vital margin of safety" against the Soviet Union. Reagan said the conduct of foreign policy "has been marked by inconsistency and incompentence."

Carter who is scheduled to address the B'nai B'rith convention today, has won praise, even from some of his critics, for his attempts to achieve a Middle East settlement. But Reagan was sharply critical of those efforts.

"There are basic ambiguities in the documents Camp David produced, both in the links between the Israel-Egyptian peace and in the provisions for an autonomous regime in the West Bank and the Gaza Strip," Reagan said. "There ambiguities have now brought negotiations to a dangerous impasse.

"Let us remember that an autonomous Palestinian Arab regime for the West Bank and the Gaza Strip was an Israeli proposal -- a major concession on Israel's part in the interest of progress for peace."

Reagan, a strong champion of Israel since its creation, said that negotiations between Israel and Jordan, without the Plo, "could result in long and creative steps toward resolving these problems."

There should be no more withdrawal of Israeli troops or changes in its security position "until Jordan and other neighbors make peace," he said.

Reagan also assailed the administration's conduct in the United Nations, particularly for abstaining rather than vetoing a resolution opposing Israeli control of Jerusalem.

"I believe this sorry episode sheds some light on an earlier action by Jimmy Carter concerning another U.N. resolution, voted on in March this year," Reagan said.

He observed that the Carter administration did not veto a "mischievous" resolution calling Israel's presence in Jerusalem an "occupation" and then, after a public outcry, changed positions.

"The man who asks 'trust me' zig-zags and flip-flops in ever more rapid gyrations trying to court favor with everyone: Israel, the PLO, the voting bloc in the United Nations and voters at home," Reagan said.

Introducing Reagan, Al Spiegel, chairman of the Coalition for Reagan-Bush, said that "long before he was a candidate for public office" Reagan had resigned from Lakeside Country Club in Los Angeles because it refused to admit Jewish members.