The House Assassination Committee will announce its latter-day verdicts on the murders of President Kennedy and the Rev. Martin Luther King Jr. Jan. 3, Chairman Louis Stokes (D-Ohio) said yesterday. The Evidence is to be made public later.

The awkward sequence was prompted by a starting last-minute acoustical study for the committee, indicating that there may have been a conspiracy behind Kennedy's assassination in Dallas 15 years ago.

The committee's experts said a Dallas police tape recording of the noises in Dealey Plaza when Kennedy was killed on Nov. 22, 1963, showed that a fourth shot was fired at the presidenial motorcade from the area of the so-called grassy knoll in front of Kennedy's limousine.

At a terse meeting yesterday, opened to the public at the last moment, the committee decided to hold a public hearing on the new evidence next Friday. It had originally been scheduled as an executive session at which members were to vote on the contents of a 600-page final report concluding, as the Warren Commission had, that Lee Harvey Oswald was the president's lone assassin.

The Warren Commission said that only three shots were fired at the president, all from behind, all from the 6th floor window of the Texas School Book Depository, where it said Oswald has set up a sniper's nest. A fourth shot from the grassy knoll in front of the president would have required the presence of a second gunman, and would strongly suggest the existence of a conspiracy.

Two acoustical experts hired by the committee in September, Mark Weiss and Ernest Aschkenasy of Queens College in New York City, said there was a "greater than 95 per cent probability" that the sounds of four gunshots are present on the tape and that the third of those shots came from the grassy knoll.

The committee had planned to keep the findings secret and disclose them only in its final report, but Rep. Harold S. Sawyer (R-Mich.) revealed them Wednesday in Grand Rapidd, Mich., during a radio interview on the committee's work.

A former prosecutor, he said the experts had concluded "beyond a reasonable doubt" that four shots were fired, including one from the grassy knoll.

"The [acoustical] evidence," Stokes announced at yesterday's meeting, "will be heard in its full context, and the possible meaning of it will be explored."

The committee, however, will barely pause before issing its "findings and recommendations" concerning the Kennedy and King assassinations on Jan. 3, the day its congressional mandate expires.

The evidence will take longer to assemble. Stokes said "the commentary" backing up the committee's findings and recommendations "and a summary of the basic evidence" compiled during the two-year inquiry will not be ready for a number of weeks, perhaps not before spring.

Stokes said he hoped this work-to be undertaken by a caretaker staff-would be done "no later than March 30." He said segments of the final report might be made public before then.

Indirectly chiding Sawyer and Rep. Christopher J. Dodd (D-Conn9), who also spoke publicly of the acoustical study, Stokes said, "It is to be regreted that information that was given to the Select Committee on Assassinations in a confidential briefing has been made public prematurely."

But the committee chairman and other members agreed they had no choice but to schedule an open hearing on the issue, since it has become "a matter of public concern."

Perplexed committee members have privately and publicly described the acousrical study as apparently "solid ... disturbing" evidence, albeit unsupported by most of the other scientific work done for them.

"It could serve as text for high school physics students for years," said Del. Walter Fauntroy (D-D.C.).

For a committee that was organized more than two years ago to set to rest the nagging doubts about both the Kennedy and King assassinations, however, it also represents a stinging rebuke to the $5.8 million inquiry, one that will leave the public more skeptical than ever.

Dodd, for one, has said he feels the door ought to be left open for a bid to continue the investigation in the next Congress, but the loose ends are more likely to be turned over to the Justice Department for further scrutiny.

"If the committee kept going," Fountroy told a reporter, "then [people] would say we held this up to the last minute to get reconstituted."

Fountroy said he wanted none of that. "I'm through, he said emphatically. "I'm through."