THE SUMMARY of the findings of the House Select Committee on Assassinations does little to resolve the controversies that have raged for more than a decade over the murders of President Kennedy and Dr. Martin Luther King Jr. Those who have believed all along that both men were the victims of "conspiracies" will be reinforced by the committee's conclusion that there must have been "conspiracies" in both cases. Those who have believed that Lee Harvey Oswald and James Earl Ray acted alone are unlikely to be shaken profoundly by the acoustical or other circumstantial evidence that the committee has relied on so heavily to support its findings. And those who have never been sure, one way or the other, are left right where they were when the committee began work two years ago -- faced with the probability that there never will be final, conclusive answers.

The committee's finding that President Kennedy "was probably assassinated as a result of a conspiracy" appears to be based solely on scientific, acoustical evidence. This evidence, the committee says, "establishes a high probability that two gunmen fired at" the president in Dallas in 1963. But the committee has no leads as to who fired the fourth bullet, no evidence to link Mr. Oswald to a second assassin.

While this basic finding seems sufficient to bolster all the theories of conspiracy that have been suggested by one investigator or another during the last 15 years, in fact it doesn't provide as much reinforcement as you might suppose. Elsewhere, the committee's report to the House says the Secret Service, FBI and CIA were not involved in the conspiracy. And the report does not offer any reason to believe, on the basis of the available evidence, that there was any involvement on the part of the Soviet or Cuban governments or the anti-Castro Cuban organizations or the national crime syndicate. That takes care of most of the organizations that have been accused, by one "conspiracy" theorist or another, of planning the assassination.

All that is left is a theory of conspiracy stripped of the international or domestic intrigue on which many of the Warren Commission's critics have focused. If the conspiracy was not the work of the agencies, governments or groups that the committee has ruled out, whose was it? No douby the next round of articles and books will dredge up another list of possibilities.

In the process, however, it is worth wondering about this easy resort to the use of the word "conspiracy" -- a word that suggests many people acting together in a political plot, with cold and careful calculation. If the committee is right about a fourth shot from the Grassy Dnoll, could it have been some other malcontent whom Mr. Oswald met casually? Could not as many as three or four societal outcasts, with no ties to any one organization, have developed in some spontaneous way a common determination to express their alienation in the killing of President Kennedy?

The flaw in the big conspiracy theories is the inability of anyone, including this committee, to find any evidence of such an organized effort. Most large conspiracies unravel because someone leaves a clue somewhere. It is the inability of the committee to present even one such clue that enables those who believe Mr. Oswald acted alone to rest their case. If the acoustical evidence is valid -- a matter about which we would still like to know more -- it is possible that two persons, acting independently, attempted to shoot the president at the same time. If the possibility of such a coincidence is slight, so is the possibility that a large group of conspirators could erase the trail so thoroughly that no trace was left behind.

The committee's findings in regard to the murder of Dr. King are less interesting because the committee has revealed so little of what it has discovered. It says, conclusively, that Dr. King was killed by James Earl Ray, and it says it believes, on the basis of circumstantial evidence, that "there is a likelihood" Mr. Ray's action was the result of a conspiracy. While it then goes on to rule out the involvement of any agency of government in that assassination, it says it will discuss in its full report (due in March) which private organizations or individuals might have been involved. That leaves nothing more to be said of its work on this case right now.

By closing out its investigation at this stage, particularly in the case of the Kennedy assassination, the committee is simply passing responsibility along to the Department of Justice. Now there may be additional investigations that the department should undertake in the King case once the committee's final report is complete. But there seems little reason for the department to use its resources exploring the dead ends and pursuing the cold trails that the committee is presenting it in the Kennedy case. The better course would be for the committee to ask the House of Representatives whether it wants a further investigation of the new acoustical evidence and the "conspiracy" finding it has triggered or whether it is prepared, however reluctantly and with whatever sense of frustration, to leave the matter where it now rests: as one of history's most agonizing unresolved mysteries.