The chief counsel of the House Assassinations Committee said yesterday he has gathered uncorroborated "information" suggesting a conspiracy in the murders of both President Kennedy and the Rev. Martin Luther King Jr.

Struggling to keep their investigation alive committee members convened yesterday in secret session for a briefing from chief counsel Richard A. Sprague and his aides on the progress of the inquiry so far.

In a short statement before the press and public were excluded, Sprague told the committee that the "information compiled to date was a blend of reports from "witnesses who have advised us directly that they have relevant information" and hearsay about "witnesses whom we have been told have information."

As a result, he added in straightface understatement, "We have been unable to do what I would consider a thorough check of the information we have been advised of."

That said, the former Philadelphia prosecutor continued, "The sum total of the information would be in the nature of evidence indicating that others may have had knowledge of or participated in arranging the assassinations of Dr. King and President Kennedy."

Sprague did not elaborate, but it seemed likely that much of the information originated with the many books and articles written in recent years in attempts to debunk the official findings that there was no credible evidence of a conspiracy in either murder. The committee's 73-member staff has been bogged down by controversy in recent weeks, cut off from classified FBI files and unable to travel or even make long-distance phone calls.

Trying to regain its momentum following the resignation of Rep. Henry B. Gonzalez (D-Tex.), who had tried to fire Sprague for alleged mismanagement and insubordination, the committee met formally yesterday for the first time under its new chairman, Rep. Louis Stokes (D-Ohio).

It has only three more weeks to win a new charter from the House and head off extinction. SPeaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) and other House leaders have predicted that the committee will probably not be continued past March 31 unless it can produce some striking new evidence or, in O'Neill's words, "something of a sensational nature."

The Warren Commission, which investigated the 1963 Kennedy assassination with the resources of the FBI and other government agencies, concluded that Lee Harvey Oswald, acting alone, killed the President. Similarly, the FBI concluded that James Earl Ray, now serving a 99-year prison term, was King's lone assassin, although a Justice Department task force recently conceded that the sources of Ray's money "still remain a mystery today."

After Sprague's brief public presentation, the committee voted 8 to 2 to go into secret session. Dissenting were Reps. Charles Thone (R-Neb.) and Harold E. Ford (D-Tenn.).

Sprague mentioned no names, not even those of Oswald or Ray, but it seemed clear that the "others" he had in mind were in addition to those two men. He also told the committee that there was some information indicating that some unidentified individuals knew in advance that the Kennedy assassination "was about to occur."

Most of yesterday's session, however, as spent on the King murder. At a lunch-hour briefing, Stokes told reporters that the committee was moving with deliberate caution, but he said there was "a very good possibility that some witnesses" may be called to a public hearing before March 31 in an effort to demonstrate the need for continuing the inquiry.

The new chairman would not discuss the witnesses who might testify, but other sources said two under consideration are Ray's brother, Jerry, and former Memphis police detective Edward E. Redditt, one of two black plainclothesman assigned to keep King under surveillance before the 1968 murder.