Having satisfied itself that Lee Harvey Oswald killed President Kennedy and that Jack Ruby killed Lee Harvey Oswald, the House Assassinations Committee yesterday began concentrating on more difficult questions.

Now in the final week of its public inquiry into the president's assassination, the committee served up a portpouri of tantalizing but inconclusive leads, some old and some new, concerning the Mafia, anti-Castro Cuban groups, and suspicious characters on the fringes of both who knew either Ruby or Oswald.

Chief committee counsel G. Robert Blakely indicated that the answers, if any, will not be forthcoming until the publication of the committee's final report at the end of the year.

Among the gleanings:

Ruby made a "suspicious" number of long-distance phone calls in the summer and fall of 1963 to various individuals linked in some way with organized crime, including associates of Mafia leaders Santos Trafficante, Sam Giancana and Carlos Marcello, and of Teamsters union president James R. Hoffa and others in the Teamsters hierarcy.

Six unidentified witnesses, "each corroborating the others," have told the committee in secret sessions that Oswald was in Clinton and Jackson, La., in late August and early September of 1963 looking for a job at East Louisiana State Hospital. Some of the witnesses have placed Oswald there with two deceased targets of New Orleans District Attorney Jim Garrison's controversial investigation of 1967-68; airline pilot David Ferrie and New Orleans businessman Clay Shaw.

"It has been suggested," Blakey added without elaboration, "that the testimony that Oswald and Ferrie were together in Clinton and Jackson is, despite the Garrison prosecution, impressive," Blakey noted that Ferrie once worked as an investigator for Carlos Marcello "who has been identified as the organized crime boss of Louisiana and Texas."

A founder of an anti-Castro commando organization called Alpha 66, Antonio Veciana Blanch, has told the committee in repeated interviews that an American can "directed him in all his activities" (including two plots to kill Castro) once met with Veciana in Dallas in August 1963. With the American was a third man whom Veciana later identified as Oswald. The American control agent, who went by the name of Maurice Bishop, has yet to be located, but Blakey said that while the committee cannot be conclusive, "It can say that Veciana's allegations remain undiscredited."

The committee is still investigating the story of Sylvia Odio, a Cuban exile whose parents were imprisoned in Havana as a result of Veciana's assassination plots. She told the Warren Commission that a man who was introduced to her as "Leon Oswald" and who looked like Lee Harvey Oswald visited her apartment in Dallas in late September of 1963 in the company of two Latin men. They wanted to know if she would finance some anti-Castro undertaking they were planning, but she declined.

The Warren Commission played down the Odio story, the committee was told, in tune with a staff attorney's memo of Sept. 19, 1964, which warned: "There are problems. Odio may well be right. The commission will look bad if it turns out that she is."

The murky trails were summed up in a lengthy 45-page opening statement which Blakey read only in part. He devoted most of his time to the "dramatic upsurge" in Ruby's long-distance phone calls in October and November of 1963 although those singled out by committee investigators as "suspicious" had their peak in August.

Blakey said that many of the October-November calls may have been related to a labor dispute Ruby was having with the American Guild of Variety Artists over "amateur nights" at his striptease clubs, but the committee counsel said that a number of the contacts cannot be "readily or easily dismissed."

Indicating that the Warren Commission glossed over the Ruby phone records, Blakey said they showed seven calls in the summer, most of them in August, to an old friend, casino gambler Lewis J. McWillie in Las Vegas. Ruby had once visited McWillie in 1969 in Havana where he was then working in "an organized-crime-controlled casino."

Other suspicious calls, Blakey reported, were on Oct. 26, 1963, to Chicago bondsman Irwin S. Weiner, "allegedly a key functionary between the Chicago Mafia and various corrupt union officials"; on Oct. 30, to a New Orleans trailer park owned by Nofio J. Pecora, a former heroin smuggler and allegedly a close associate of Carlos Marcello; on Nov. 7 and again on Nov. 8 to Hoffa's top lieutenant and reputed "enforcer," Robert B. (Barney) Baker of Chicage, and again on Nov. 8 to Murray W. (Dussy) Miller, head of the southern conference of Teamsters.

Weiner, Miller and Baker all told the committee that Ruby had been seeking their help in his labor dispute with the ABVA, but Blakey pointed out that Weiner had once told another story to a reporter and Baker never mentioned the second Ruby call when he was questioned by the FBI in 1964.

The witnesses of yesterday's hearing included Ruby's younger brother, Earl, who said he was convinced Jack Ruby acted impulsively, angered by a "smirk" on Oswald's face.

Earl Ruby, however, could not satisfy the committee about an April 1, 1962, telegram that had apparently been sent to Havana, Cuba, from Earl Ruby's business establishment, Cobo Cleaners, in Detroit. Weeks ago, he told the committee no one else but he would have sent such a message, but yesterday he insisted that he never sent a telegram to Havana. He suggested that the billing actually reflected a wire to Cuba, N.Y. or one of the five other states that has a town called Cuba.

Ruby family lawyer Alan Adelson told the committee that Ruby's latter-day mutterings that the truth would never come out could be dismissed as the ravings of a man who had slipped into paranoia, convinced that all the Jews in the county were bring shipped to Dallas to be killed in retribution for his killing Oswald.

The final witness, Capt. Jack Revill of the Dallas police department, dismissed Ruby as a "buffoon" and asserted that "if Jack Ruby was a member of organized crime, then the personnel director of organized crime ought to be replaced."

One of the officers assigned to investigate how Ruby got into the basement of police headquarters on Nov. 24, 1963, when he killed Oswald, Revill said, "the entire (Dallas Police) department was negligent," but he acknowledged that no single officer was ever disciplined. Revill said he now thinks Ruby may have slipped into the basement through an untended door instead of strolling down a vehicular ramp as investigators had assumed.