House Democratic leaders yesterday endorsed a long-shot attempt to salvage the investigation of the murder of the Rev. Martin Luther King Jr., but offered less hope for the inquiry into the assassination of President Kennedy.

Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said after a meeting with Democratic members of the embattled House Assassinations Committee that they are hoping to stage a hearing on the King murder to dramatize that investigation before the committee's charter runs out March 31.

The committee's already shaky prospects for survival were damaged even further Wednesday when Chairman Henry B. Gozalez (D-Tex) submitted his resignation as an out-growth of his dispute with the committee's chief counsel, Richard A. Sprague.

O'Neill said he'd been told at yesterday's conference with the committee's seven other Democrats that "there are three witnesses who are ready to appear" about the King assassination in Memphis in 1968.

He said he did not know how compelling their testimony might be, but said he had been "led to believe that it's information the American public would be keenly interested in."

The Speaker declined to say whether he feels the House should vote to continue the Assassinations Committee past the end of the month. When asked that question, O'Neill said only.

"Well, let's just see what we're talking about with these three witnesses."

O'Neill said he did not know if James Earl Ray, who is erving a 99-year prison term for King's murder, was one of the putative witnesses, but other sources said he is not. One source said committee members were talking of calling one of Ray's brothers and two other witnesses.

Gonzales, who has been sick with the flu in his San Antonio home for the past two weeks, has yet to return O'Neill repeated phone calls. But the Speaker said he will do nothing about the resignation until he has had a chance to talk with the unwilling chairman.

If Gonzalez remains adamant, it is up to the House to accept or reject his resignation, but O'Neill would not discuss when he might schedule the issue for floor action.

Committee Democrats, meanwhile, said they would take steps to call a meeting for Monday, with or without Gonzalez, in order to recommend a proposed budget for the rest of the year, adopt rules of procedure and authorize February paychecks for the committee's 73-member staff. The salaries have been held up in Gonzalez absence because of $3,000 in excess spending for the month.

The ranking Democrat on the committee, Rep. Richard Preyer (D.N. C.), acknowledged after meeting with the Speaker and other House leaders that "the odds (on the committee's survival) are long right now in view of all the problems that have come up."

Preyer, who said he does not want to be chairman if the committee is continued, added that "one of the problems the committee must resolve are the charges against Mr. Sprague," whom Gonzalez has accused of mis-management and insubordination. Other committee members, however, said the Sprague dispute would not be on Monday's agenda, and they voiced until the committee recovers its equilibrium.

Aides to Gonzalez said the committee's refusal to face up to the issue was a primary factor in his decision to resign.

House Majority Leader Jim Wright (D-Tex.) said he did not know when a hearing on the King murder might be held, but said he thought the chances of the committee's surviving at all were not much more than 10 per cent.