House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) will lead a bipartisan congressional delegation to Moscow next month for talks that are expected to include a meeting with Mikhail Gorbachev, the new Soviet leader, sources said yesterday.

The O'Neill mission is a followup to a recent U.S. tour by officials of the Supreme Soviet. A small group of officials led by Politburo member Vladimir Shcherbitsky met President Reagan at the White House March 7, setting a precedent for an O'Neill-Gorbachev meeting.

"A meeting with Gorbachev was requested," one source said, but "the schedule has not been firmed up yet."

About 12 members of Congress and their spouses are scheduled to go to Moscow and Leningrad April 7-12. House Minority Leader Robert H. Michel (R-Ill.) is to be among the group. Assistant Secretary of State Richard R. Burt briefed members of the delegation yesterday at the Capitol, and a congressional source said the State Department is "highly supportive" of the trip.

Plans for the congressional mission became known as the administration called three Soviet military attaches to the Pentagon to express what an official termed "our sense of outrage" over the killing of a U.S. Army officer by a Soviet sentry in East Germany on Sunday.

The Pentagon said the body of Maj. Arthur D. Nicholson Jr. would be flown to the United States today. Nicholson is to be buried Saturday afternoon at Arlington National Cemetery, officials said.

"We continue to believe the shooting was an outrageous, unnecessary and totally uncalled for act," a State Department spokesman said. "We hope the new Soviet leadership will seize this opportunity for constructive actions that will prevent such incidents in the future."

After Wednesday afternoon's State Department meeting of U.S. and Soviet diplomats about the case and the discussions with the Soviet attaches yesterday at the Pentagon, the administration is "in a holding pattern" on the shooting, waiting for a response from Moscow, according to a State Department official.

An official familiar with the discussions said there has been a distinct change in the tone of the Soviets since early statements blaming Nicholson for the incident. Another official said it was a good sign that no public statements about the case have been issued from Moscow since Tuesday.

Details of the shooting, based on a full interview with Nicholson's driver, Sgt. Jesse Schatz, make it clear that the U.S. officer never reached the storage shed he intended to investigate, did not open a window or take a picture of the interior, according to Pentagon sources.

The sources said it is clear that Schatz and Nicholson did not go through a restricted area, off-limits to U.S. observers, on their way to the area.

Despite earlier statements, officials at the State and Defense departments said the site of the killing had not been designated as a temporarily restricted area by the Soviets at any time in the recent past