Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.) urged President Reagan yesterday to seek support from American Jewish leaders for his embattled proposal to sell missiles to Saudi Arabia and said later that Reagan thought it was "a good idea."

Although they oppose the proposed sale, American Jewish groups did not wage an all-out campaign against it during last week's congressional debate, which resulted in overwhelming defeat for Reagan's proposal in both chambers. Reagan is expected to veto the congressional rejections later this week and is gearing up a campaign to sustain the veto in the Senate.

Lugar, at a White House meeting, said Reagan should approach Jewish leaders and Israel to support the aid package on grounds that it would be important for U.S. policy and Israel's security to have good relations with moderate Arab states.

"I would not be at all surprised if the president did not try to make an appeal to the country and specifically to the Jewish leadership," Lugar said. "I think he thought that was a good idea."

A senior White House official said that the administration is taking Lugar's idea "very seriously" and that a White House effort is being planned to generate support for the package by Jewish leaders.

Reagan continued pressing key senators at two meetings yesterday and was told that he faces an uphill fight. "It's tough," Majority Leader Robert J. Dole (R-Kan.) said. Lugar added, "It's a very uphill struggle."

White House officials said Reagan was planning to make the point to a small group of senators yesterday that Saudi Arabia had been helpful privately after the U.S. bombing of Libya.

Officials said the Saudis had played a key role in "torpedoing" a call by Libyan leader Muammar Qaddafi for an emergency Arab League summit to impose sanctions against the United States for the attack April 15.

The summit was postponed after disagreements on the agenda. News reports from the region quoted diplomats as saying that it was unlikely that Arab leaders would have approved Qaddafi's call for an oil embargo against the United States and other sanctions.

A White House official said the Saudis had "blocked" the Qaddafi move. White House spokesman Larry Speakes has also described the Saudi statement criticizing the U.S. attack as "a mild reaction in the Arab world, and we don't have any major problems with it."

Speakes quoted the president as telling Republican congressional leaders yesterday that rejection of the $354 million Saudi arms package would "undermine the credibility of all our security commitments in this critical region of the world."

Reagan said rejection would "send a signal throughout the Middle East to the clear detriment of our interests there for many years to come."

The Republican-controlled Senate voted 73 to 22 against the sale; the House voted 356 to 62 against it. The White House is concentrating its efforts in the Senate, where it needs 34 votes to sustain a veto.

Lugar said that sale advocates need 11 more votes and that Sen. Nancy Landon Kassebaum (R-Kan.), absent last week, would support it.

The president met yesterday with Republican Sens. Ted Stevens (Alaska), Chic Hecht (Nev.), Paul S. Trible Jr. (Va.) and Steve Symms (Idaho).

Referring to Hecht, Trible and Symms, who voted against the sale, Lugar said, "They are all inclined to help if they can, but they expressed several concerns. They didn't turn the president down. On the other hand, no one came out and declared that they were changing."

Alan Cranston (D-Calif.), leader of Senate opposition to the sale, told reporters yesterday, "I don't flatly predict victory, but I think our chances are as good as" Reagan's.

"The Congress has never turned down an arms sale or defeated President Reagan on a veto of a major issue, so it will be tough. But I think most of our votes are solid," Cranston said.