Interior Secretary James G. Watt cautioned in a letter last month to Israeli Ambassador Moshe Arens that American support for Israel could be jeopardized if "liberals of the Jewish community join with the other liberals of this nation" in opposing the Reagan administration's accelerated energy development policies.

The Watt letter, disavowed and termed "unfortunate" by the White House yesterday, warned that unless the United States reduces its reliance on foreign energy sources "there is great risk that in future years America will be prevented from being the strong protector and friend of Israel that we are and want to be."

Watt wrote that "the friends of Israel" should support the Reagan administration's energy policies "if they really are concerned about the future of Israel."

These policies include Watt's controversial programs to expand offshore oil drilling and coal mining on public lands, which have recently come under sharp attack from Democrats, environmentalists and officials of several affected states.

"If the liberals of the Jewish community join with the other liberals of this nation to oppose these efforts, they will weaken our ability to be a good friend of Israel," Watt wrote in a June 17 letter. "Your supporters in America need to know these facts."

The letter triggered an angry reaction yesterday from American Jewish leaders who variously called it "inappropriate" and said it was "deeply offensive" to appeal for American Jewish support through a foreign ambassador.

They said they also resented the implication that American Jews should take positions on the Reagan administration's domestic policies because of concern for Israel.

A White House spokesman said that Watt's remarks, made in a letter entitled "A Personal Communication" to Arens, "in no way reflect the United States' foreign or domestic policy."

Assistant White House press secretary C. Anson Franklin said: "Secretary Watt's unofficial letter to Ambassador Arens represents his own personal views. The White House regards his remarks as unfortunate."

Watt's press secretary, Douglas Baldwin, did not return repeated telephone queries about the letter yesterday. The letter was written after a personal conversation between Watt and Arens at a Bonds for Israel dinner at the Washington Hilton, according to an Israeli Embassy official.

The Interior Department's public affairs office sent a copy of the letter to Cable News Network in advance of Watt's appearance Thursday night on the CNN program "Crossfire." Tom Braden, co-host of the show with Pat Buchanan, said the letter arrived with a sheaf of statements and speeches by Watt. Braden made a copy of the letter available to The Post.

When Braden asked Watt on the air about the views expressed in the letter, the secretary answered, "Right on! Right on!" In response to Braden's suggestions that the letter reflected bigotry, Watt said: "If you want to call yourself a bigot, you do it. I'm not going to do it."

Jewish leaders said yesterday that they have long shared Watt's view that the United States should speedily reduce its reliance on imported oil and that such an approach will benefit Israel as well as other American allies. But they said they do not believe it follows that they should support Watt's and Reagan's policies.

"First of all, I don't like being appealed to as a Jew on an issue that is essentially of concern to all Americans," said Rabbi Alexander M. Schindler, president of the 1.5 million-member Union of American Hebrew Congregations. "Secondly, Moshe Arens is not our foreign minister. We are Americans. Secretary of State George P. Shultz is our foreign secretary."

"I find it politically and morally offensive," said David Saperstein, who heads the Interfaith Coalition on Energy, made up of Protestant, Catholic and Jewish leaders. "I hear a veiled threat that the administration might cut back its support for Israel if Jewish liberals do not remain quiet about energy policies, even if they think these policies are bad for America and bad for humankind."

"He would have been better advised to go to the leadership of the Jewish community lest he unwittingly contribute to this notion that the American Jewish community takes orders from a foreign embassy," said Hyman Bookbinder, a longtime official of the American Jewish Committee.

But Bookbinder added: "It isn't such a great error he made. I just wish he hadn't done it that way. Of course we have a special affinity and concern for the state of Israel. We are Americans who are Jewish."

The Jewish leaders stressed that their support for energy independence predates the 1973 Yom Kippur War and the resulting six-month Arab oil embargo that focused national attention on the issue. The American Jewish Committee created a national energy committee in 1972, Bookbinder said.

The letter came at a particularly sensitive time for American Jewish leaders, who said the recent Middle East war has triggered unfair suggestions that Jews have divided loyalties between the United States and Israel.

Arens apparently did not convey Watt's message to American Jewish leaders. "He's had other priorities for the last few weeks," one of the leaders said, referring to the fighting in Lebanon. Bookbinder, Schindler, Saperstein and Howard Squadron, president of the American Jewish Congress, said Arens had not mentioned it to them.

Israeli Embassy counselor Benjamin Avileah said Arens answered Watt's letter, but he declined to discuss the response. "It's not our policy to make public correspondence between us and the officers of the Cabinet of a host country," he said.

The letter was written one month before Watt released his controversial plan to make 1 billion acres of coastal waters available for offshore oil and gas drilling in the next five years.

After avoiding national press attention for several weeks, Watt appeared on three national television programs this week to tout the plan as strategically essential and environmentally safe.

Watt closed his letter by saying he hoped to speak to "groups of your supporters in this nation so that I might share with them the truth of what this administration is trying to do for America and the free world."

The letter indicates that a carbon copy was sent to Sen. Rudy Boschwitz (R-Minn.), who also attended the Bonds for Israel dinner.

Boschwitz said he did not recall receiving the copy, but said he saw nothing wrong with the letter.

"What the hell? It's a free country," Boschwitz said. "He can write a letter to anybody he wants."