The House Assassinations Committee concluded yesterday in a stunning wrapup of its two-year investigation that President John F. Kennedy "was probably assassinated as the result of a conspiracy."

Convinced by a new acoustical study of the noises in Dallas' Dealey Plaza where Kennedy was killed on Nov. 22, 1963, the committee agreed "the evidence establishes a high probability that two gunmen fired" at the president that day within a split-second sequence.

The members of the panel, headed by Rep. Louis Stokes (D-Ohio), acknowledged that they have no idea who that second gunman might have been.

"The committee is unable to identify the other gunman or the extent of the conspiracy," it said.

The House investigators, however, appeared to be leaning toward the notion that a metley assortment of gangland figures or anti-Castro Cubans, or both, might have been involved.

The assassinations Committee said it also believes, "on the basis of circumstantial evidence available to it, that there is a likelihood that James Earl Ray assassinated Dr. Martin Luther King as a result of a conspiracy." But it offered no reasons for that terse conclusion.

The findings of the $5.8 million inquiry were made public in a spare, 17-page summary that Stokes addressed to the clerk of the House, Edmond L. Henshaew. A complete report, including the evidence and scientific studies the committee relied upon, will be published in segments in the weeks ahead. Stokes indicated that the committee has yet to deal with the problem of securing "the declassification of classified information" for the final report.

The House committee said it still felt that Lee Harvey Oswald fired the shots that killed the president from a perch in the Texas School Book Depository, but it directly contradicted the Warren Commission's finding in 1964 that Oswald acted alone.The report chided the commission for pretending to certainties that were not justified.

Evidently anxious to avoid similar criticism, the Assassinations Committee dealt gingerly with a number of the conspiracy theories that have swirled about the Kennedy assassination for years. Before the acoustical study was presented to it just 13 days ago, the committee had been on the verge of concluding that Oswald, whatever his motivations, was the only gunman in Dallas that day.

In any case, the committee said it believes, "on the basis of the evidence available to it," that neither the Soviet nor the Cuban government was involved in Kennedy's murder.

Similarly, it said, "on the basis of the evidence available to it," that it did not think "anti-Castro Cuban groups, as groups . . . [or] the national syndicate of organized crime, as a group" was implicated.

"But the available evidence," yesterday's report said of both anti-Castro activists and members of organized crime, "does not preclude the possibility that individual members may have been included."

By contrast, the committee stated flatly that neither the Central Intelligence Agency, the FBI nor the Secret Service was involved in the Kennedy assissination. It also said that "no federal, state or local government agency was involved in the assissination of Dr. King".

There was no indication in the 17-page submission to the House whether any of the committee's 12 members dissented from the finding. The panel met in executive session Friday night to vote on the report.

The Justice Department, the Secret Service the CIA, the FBI and the Warren Commission were all criticized in connection with Kennedy's death - the Secret Service for failing to protect him adequatly, the CIA for keeping secrets both before and after the assassination, and the others for short comings in the original investigation.

In dealing with the Kennedy assassination itself, the committee was plainly convinced that the belatedly discovered shot from the so-called grassy knoll in Dealey Plaza - in front and to the right of the presidential motorcade - hit no one.

"Lee Harvey Oswald fired three shots at President John F Kennedy," the committee stated, as did the Warren Commission before it. "The second and third shots he fired struck the president. The third shot he fired killed the president."

The evidence of a fourth shot, fired just five-tenths of a second before the last bullett from Oswald's rifle, came from a Dallas police recording made at the time of the assassination when a motorcyle patrolman, H. B. McLain, inadvertently turned his transmitter on. The original polyester Dictabelts were available at the time the Warren Commission did its work, but apparently no one through to submit them to acoustical anaylysis.

At a public hearing Friday, the committee's chief counsel, G. Robert Blakey, said it learned more than a year ago, in September of 1977, of the possibility of obtaining important evidence from the recording

He was apparently alluding to an Aug. 22, 1977, newsletter put out by one of Warren Commission's crities, Penn Jones of Midlothian, Tex., which dealth with a tape copy of the original recording and contended that it showed as many as seven shots.

Blakey, however, said "no audio sounds could be discerned" on the copy the committee initially got. He said his staff finally located the original dispatch tape and Dictabelts with the help of a retired Dallas police official.

A study by the Cambridge, Mass., firm of Bolt, Beranek & Newman found, after test firings in Dealey Plaza this past August to compare against the original noises, that there were firm signs of three shots, all from behind, and a 50-50 probability of a fourth, from the grassy knoll.

Chagrined by the ambivalence, the committee commissioned acoustical experts Mark Weiss and Ernest Aschkenasy of Queens College in New York City to conduct a more exhaustive study of the noise from the grassy knoll. They told the committee first in secret session Dec. 18 and finally in public on Friday it was "beyond a reasonable doubt" that a fourth shot had been fired from the grassy knoll.

Dismissing suggestions that the noise might have stumbled onto the police frequency from some other location in Dallas Weiss and Aschkenasy said the echoes is caused created a unique signature that could only have come from a motorcyle located in Dealey Plaza approximately 120 feet behind the presidential limousine. They tracked the supersonic sound with precise measurements from the grassy knoll to nearby buildings and obstacles, through the motorcyle's windshield, to a transmitter on the left side of the vehicle. The long-unknown driver, Officer McLain, was located as a result of the work.

The study left the committee, which had been set up in the fall of 1976 to resolve nagging doubts about both the Kennedy and King assassinations, in a quandary.

As one of the committee's members, Rep, Floyd J. Fithian (D-Ind.), observed unhappily at Friday's public hearing. "we may be in a position of having raised more serious questions than we answered as a committee."

The finding of a probable conspiracy, based on the assumption that an other gunman firing at the same time as Oswald hat to be associated with him stands out in the summary like a last-minute insert. But as it states, in addition to the acoustical evidence, "other scientific evidence does not preclude the possibility of two gunman firing at the president." Beyond that, as Blakey states at Friday's hearing, while most witnesses who had an opinion as to where the shots came from thought they came from the Book Depository, not a few others, 21 in all, though they had come from the grassy knoll.

"I have no doubt about it," one of them, S. M. Holland, told the Warren Commission years ago, adding that he saw a puff of smoke as well. "I have no doubt about seeing that puff of smoke come out from those trees either."

One Dallas motorcycle officer threw down his cycle in the middle of the street and ran up, gun drawn, toward the stockade fence - where the experts say the shot was fired. There, as Blakey related yesterday, he encountered a man "who identified himself as a Secret Service agent and was allowed to pass on."

The committee did not dwell on its reasons for not precluding anti-Castro or gangland figures from potential involvement in the assassination, but it has explored evidence that reputed Mafia leader Santo Trafficante once predicted the president would be "hit," in retribution for the Kennedy administration's campaign against Teamsters Union leader James R. Hoffa. At another point, the committee authorized a subpoena from reputed Mafia leader Carlos Marcello of New Orleans, but never called him.Blakey has repeatedly refused to explain why.

Sources quoted by the Associated Press said the committee's final report would cite testimony from residents of Clinton. La., who say Oswald once traveled there in 1963 with the late David Ferrie, an airline pilot and private investigator from Marcello's criminal lawyer. Ferrie was a traget of former New Orleans District Attorney Jim Garrison's baroque 1967-68 investigation into the assassination.

Ferrie, before his death, said he felt he was the victim of a "witchhunt."

He also spoke vehemently against the Kennedy's but he denied ever knowing Oswald.

In its finding on the King assassination, the committee concluded that James Earl Ray murdered the civil rights leader in Memphis, Tenn., on April 4, 1968, with a single rifle shot. The report also said it was "highly probable that James Earl Ray stalked Dr. King for a period immediately preceding the Assassination."

In finding "a likelihood" of conspiracy behind King's murder, the commitee was evidently alluding to a much-publicized theory that a $50,000 price had been put on King's head by two St. Louis businessman, both now dead, and that word of the bounty eventually made its way to the Missouri State Penitentiary where Ray heard about it and acted on it even though he never collected the money.

At its public hearings, the committee has also suggested that Ray may have had help in escaping from prison in 1967 from his brother, John, and that John and another brother, Jerry, may have known of their brother's intention to kill King and helped him along the way. But the evidence has been far from conclusive.

Despite all the loose ends, the committee is scheduled to go out of business Wednesday. Stokes and other members have made clear they have no intention of trying to keep the inquiry going. Instead, in addition to a wide variety of legislative recommendations including firm charter legislation for the FBI and CIA, the committee recommended that the Department of Justice investigation is warranted in either case."