Three members of the House Assassinations Committee are challenging the panel's conclusion that the killing of Presient Kennedy was probably the result of a conspiracy.

In dissenting views that he made public yesterday, Rep. Harold S. Sawyer (R-Mich.) said he regards as "unpersuasive" the acoustical evidence of a second gunman Dallas' Dealey Plaza when Kennedy was killed in 1963.

Sawyer also challenged the committee's conclusion that the Rev. Martin Luther King Jr.'s murder in 1968 may have been the result of a conspiracy. The Michigan Republican said he felt this finding was based on "totally fabricated" testimony about a $50,000 bounty on King.

Rep. Robert W. Edgar (D-Pa.) said he and Rep. Samuel L. Devine (R-Ohio) intend to file "dissenting views" of their own concerning the committee's finding of a probable conspiracy in the president's murder on Nov. 22, 1963.

Edgar called the scientific studies of the sounds Dealey Plaza that day "interesting and professionally done," but "not good enough to jump to the conclusion that there was a conspiracy."

Devine could not be reached for comment. One of his aides said Devine would submit "additional comments," but declined to call them a formal dissent.

The Assassinations Committee voted 5 to 2 last month to adopt its report on the assassinations after three acoustical experts testified there was a 95 percent probability a second gunman had fired at Kennedy from the area of the so-called "grassy knoll" in Dealey Plaza. The Warren Commission concluded in 1964 that three shots were fired at the president, all coming from the sixth floor of Texas School Book Depository where Lee Harvey Oswald set up a sniper's nest.

Edgar was the only committee member who took issue with the accoustical findings in the committee's formal voting. He said the other "no" vote came from Rep. Christopher Dodd (D-Conn.) who wanted more testing of the sequence of shots from Oswald's rifle. Devine left the meeting before the vote, and his proxy was cast in favor of the report by Chairman Louis Stokes (D-Ohio).

Sawyer, who initially disclosed the acoustical findings on a grand Rapids radio program Dec. 20, said at the time he knew of no reason not to accept them. He did not attend the hearing at which the experts testified Dec. 29 and did not take part in the executive session voting that followed.

In his dissent yesterday, Sawyer said he doubted the tapes authenticity and suggested that the police motorcycle whose stuck transmitter picked up the sounds was several miles away from Dealey Plaza.

Noting the contention of Dallas police officials that sirens were immediately activated for the ride to Park land Hospital after the shooting, Sawyer pointed out that no sirens can be heard on the tape for almost two minutes after "what is interpreted by the acoustical experts as shots."

Beyond that, he said, "the tape, or more properly, the dictabelt which is the basis of the acoustical testimony is now 15 years old, its chain of custody is less than certain and it has been played a wholly indeterminate number of times." Over the past 15 years, Sawyer protested, "no other evidence or even what might be termed a 'scintilla' of evidence has been uncovered which would substantiate a conspiracy or which tends to negate the fact that Oswald acted alone."

The Dallas police officer whose transmitter was said to have been stuck. H. B. McLain, lagged behind the motorcade as it sped off to Parkland, according to photos taken at the time, and evidently caught up with it later. Committee lawyers have suggested this may be the reason sirens cannot be heard immediately.

In addition, a Dallas police department plan for the motorcade, dated Nov. 21, 1963, indicated that only three motorcycle officers, forming an advance unit in front of Kennedy's parade, were to use "sirens when needed." McLain was not one of them.

Taking issue with the scientific tests conducted by Mark Weiiss and Ernest Aschkenasy of New York City, Sawyer argued that their "firm conclusion" of 20 to 1 odds in favor of a shot from the grassy knoll was simply a "bootstrap analysis" of an earlier study that showed only a 50-50 probability of such a shot.

Weiss and Aschkenasy said yesterday, however, that they relied on the earlier work only to determine the echo patterns in Dealey Plaza for a shot from the grassy knoll. Far from assuming the motorcycle was where the earlier study had placed it, as Sawyer charged, they said they fixed its location with much more precision, in a slightly different spot. According to the earlier study, the tape also showed three other shots, all coming from the school book depository.