President Reagan's arrival here for the superpower summit was marred by the eruption of a bitter battle within the administration over the unauthorized disclosure of a letter to Reagan from Defense Secretary Caspar W. Weinberger. One White House official said the leak was viewed as an attempt to sabotage the summit.

The three-page letter from Weinberger warning the president of the dangers of continued adherence to the SALT II treaty was delivered to the White House on Wednesday as the cover to a long-awaited study of Soviet arms control violations. Copies were obtained Friday by The Washington Post and The New York Times, The Times printed a full copy of it in Saturday's editions.

Pentagon officials said yesterday that the Defense Department had not been the source of the leak, and an official traveling with President Reagan said that Weinberger had ordered an investigation into the matter.

Officials said that Reagan, en route to Geneva, summoned aides to a midair conference in an attempt to determine whether Weinberger or one of his aides had leaked the letter. A senior official aboard Air Force One was asked whether he regarded the leaked letter as an effort to sabotage Reagan's summit with Soviet leader Mikhail Gorbachev.

"Sure it was," the official replied.

Another senior official called release of the letter "egregious" and said it was "a blatant attempt to undermine the president just before the summit," which begins here Tuesday.

But Weinberger's spokesman, Bob Sims, denied that the secretary of defense was responsible for the disclosure.

"Department of Defense had nothing to do with the release of the text of Secretary Weinberger's letter to the president to any publications," Sims said. "It is Secretary Weinberger's longstanding policy not to discuss or make public his advice or recommendations to the president."

White House spokesman Larry Speakes told reporters en route to Geneva that the president was well prepared for the summit and in "an upbeat mood" but also angry about the disclosure of the Weinberger letter.

"The president would have preferred to read it in the privacy of the Oval Office and not in The New York Times," Speakes said.

Speakes also commented on a report that the Soviets had decided to allow 10 Soviet citizens to reunite with their families in the United States, saying that the administration was "pleased" with this news. National security adviser Robert C. McFarlane agreed but added, "As much as we welcome these, we must remain concerned with those whose separations continue."

The disclosure of the Weinberger letter once more brought into the open the bitter differences that have afflicted arms control policy throughout the Reagan administration. Until the Weinberger letter was released, these battles had subsided in advance of the summit.

Both the United States and the Soviets have pledged not to undercut the provisions of the SALT II treaty, which was signed in 1979 but withdrawn from Senate consideration and never ratified after the Soviet invasion of Afghanistan.

The Soviets have proposed continuing adherence to SALT II provisions for another year after the treaty expires at the end of 1985. White House officials said that the president has made no decision, but some administration officials have said that Reagan and Gorbachev might agree to continue respecting the treaty's provisions.

In his letter, Weinberger said that Soviet violations of existing treaties "put us in a particularly vulnerable and dangerous position when these violations are compared with the sharp reductions in our requests for strategic defense funding."

Weinberger wrote Reagan that at Geneva "you will almost certainly come under great pressure to do three things that would severely limit your options for responding to Soviet violations."

He listed these three pressure points as a demand to continue adherence to SALT II, restriction of missile defense research and a Soviet proposal for a statement "that obscures their record of arms control violations by referring to the 'importance that both sides attach to compliance.' "

Weinberger is not a member of the U.S. delegation attending the summit, although several administration officials said he wanted to be included in the official party. He is represented here by two senior advisers, Undersecretary Fred C. Ikle and Assistant Secretary Richard N. Perle, a Pentagon arms control specialist who is a longtime foe of SALT II.