Assuaged by the last-minute resignation of the chief counsel of the inquiry, the House voted yesterday to continue its beleaguered investigation into the murders of President Kennedy and the Rev. Martin Luther King Jr.

The vote, after nearly four hours of spirited and some times testy debate, was 230 to 181. By all accounts, the outcome might have been just the reverse if the chief counsel of the House Assassinations Committee, Richard A. Sprague, had not resigned around midnight in an effort to blunt the opposition.

In a short letter dictated from the offices of committee Chairman Louis Stokes (D-Ohio) late Tuesday night, Sprague said he was quitting immediately "with the hope that the Congress can now proceed with the challenge of seeing that these investigations are pursued promptly."

The decision followed gloomy reports from committee members who had taken an unofficial head count of the House to determine the prospects for passage of the resolution keeping the inquiry alive for the remainder of the 95th Congress. The committee had been scheduled to go out of business tonight without a fresh vote of approval from the House.

"We were short, clearly short," perhaps by as much as 25 to 30 votes, Rep. Christopher J. Dodd (D-Conn.) told reporters.

A switch of 25 votes would have killed the committee. In a brief news conference last evening, Chairman Stokes said he felt that Sprague's resignation "made the difference."

Moments later, Stokes abruptly cut short the news conference in apparent annoyance over continued questioning about the importance of George de Mohrenshildt, 65, to the Kennedy investigation.

A Russian-born geologist who was acquainted with Lee Harvey Oswald and who had been questioned by the Warren Commission, de Mohrenschidt was found dead Tuesday, an apparent suicide, at his daughter's oceanfront home in Manalapan, Fla.

Although de Mohrenschidt had spent three months in psychatric wing of Parkland Memorial Hospital in Dallas last fall and winter, Stokes and other committee members said they regarded him as "a crucial witness."

Rep. Richardson Preyer (D-N.C.), chairman of the subcommittee investigating the Kennedy assassination, said hints of what de Mohrenschidt might say, furnished to the committee last month by Dutch journalist Willem Oltmans, indicated that de Mohrenschidt may have talked with Lee Harvey Oswald in advance about the President's assassination. Preyer indicated, however, that de Mohrenschidt did not come up with the "unconfirmed" story until recently, after his release from the hospital.

At his press conference in the House radio-TV gallery, Stokes repeatedly refused to give any indication of why de Mohrenschidt's testimony would have been so "crucial." He finally walked out after passing over a question as to whether the committee or its staff had ever talked to the man.

[According to the Associated Press, the Palm Beach County sheriff's office reported that Gaeton Fonzi,a staff investigator for the House Assassinations Committee, went to the home of the daughter, Mrs. Charles Tilton II, at about noon Tuesday and asked to see de Mohrenschidt.]

[Tilton told Fonzi that de Mohrenschidt was not at home and Fonzi left, saying he would return that evening. De Mohrenschidt was found dead several hours later, before Fonzi's return.]

Before the showdown on the House floor, members of the Assassinations Committee met in emergency session yesterday morning to accept Sprague's resignation reluctantly and praise him for his service. The former Philadelphia prosecutor, who had stirred controversy over his proposed budget, his planned investigating techniques and finally his confrontation last month with former Committee Chairman Henry B. Gonzalez (D-Tex.), had already left Washington. He reportedly went to Philadelphia and then left on a quick vacation.

In his absence yesterday morning, he was widely hailed by committe members for remaining silent in the face of "defamatory accusations" and praised as an "outstanding public official" who had been unfairly maligned.

In indignant tones, Rep. Stewart B. McKinney (R-Conn.), contended that Sprague had been the victim of latter-day McCarthyism, a reference to the tactics of Sen. Joseph R. McCarthy during the 1950s.

"I was a child of the McCarthy era," McKinney declared. "I think that in the case of Richard Sprague, we have seen a witchhunt and a devastation of human rights that I never expected to see again."

With Rep. Charles Thone (R-Neb.), a strong supporter of Sprague, voting nay, the committee decided by a vote of 11 to 1 to accept Sprague's resignation reluctantly, in the interest of keeping the inquiry alive.

Hours later on the House floor, critics of the assissinations inquiry hurled the suggestions of McCarthyism back at the committee.

Rep. Charles E. Wiggins (R-Calif.) was especially critical of the committee's calling Florida mobster Santo Trafficante to a public hearing this month when it had been alerted in advance that he would refuse to testify by invoking the Fifth Amendment and other constitutional rights.

Brandishing a copy of the Assassinations Committee's 14-page progress report including various leads it is investigating, Rep. John D. Dingell (D-Mich.), said it contained "not one smidgin of evidence" that impressed him. He said the investigation reminded him of the days of the old House Un-American Activities committee which brought "shame upon the House" before ti was finally disbanded.

Warning the House of the possible consequences of killing the committee, Rep. Richard Bolling (D-Mo.) said the public would take it as a cover-up.

"They're uneasy, to put it mildly, about the Warren report," Bolling said. "They're uneasy about the King murder."

In an emotional highpoint that drew sustained applause, Rep. Lindy Boggs (D-La.) recalled the service of her late husband, Rep. Hale Boggs, on the Warren Commission, and went on to explain how important she thought it was to continue the investigation. She said the commission, in languages perfected by her husband, concluded only that it saw no evidence of a conspiracy in the Kennedy assassination, "according to the evidence presented . . . "

Stokes said he anticipates no trouble in obtaining the $2.7 million budget the committee is seeking for calendare year 1977.

De Mohrenshidt's death, reportedly from the blast of a shotgun placed in his mouth, caused reverberations throughout the day. In releasing a previously secret, transcript to show Sprague's rebuttal of various charges against him, the committee also made public, perhaps inadvertently, a March 17 account of evidently matters.

In it, Sprague said that de Mohrenschildt went to the Netherlands with Dutch journalist Oltmans recently. "The purpose of his (de Mohrenschildt's) trip was to divulge for the first time his knowledge of the assassination of the President, and he indicated that he was responsible for Oswald's activity, and that there were others inolved who were involved in the actual shooting of the President," Sprague told the committee.