The National Football League violated federal antitrust laws by refusing to allow the Oakland Raiders to move to the Los Angeles Coliseum, a six-member jury decided yesterday in a federal court in Los Angeles.

In this second trial of what also had become a personal confrontation between National Football League Commissioner Pete Rozelle and Oakland owner Al Davis, the jury deliberated for 5 1/2 hours after 21 days of testimony before returning its verdict favoring the Raiders and the Los Angeles Coliseum Board, which originated the suit in 1978.

The jury found that Section 4.3 of the NFL constitution, requiring a three-quarters vote to approve a franchise move, violated the Sherman Antitrust Act by unreasonably prohibiting competitive movement of teams.

Whether the Raiders will play their home games in Los Angeles this season was unclear last night. Rozelle said the league would appeal the case to the Supreme Court, if necessary. Patrick Lynch, an attorney for the NFL, said the initial appeal will be made to the 9th U.S. Circuit Court of Appeals.

The jury also decided in favor of the Raiders in the second point of the case, a claim of violation of implied faith and fair dealing. That claim was based on Davis' contention that he had an implied agreement with the league two years ago that he could move the team.

"Jackie Gleason said it better than Shakespeare or Homer--'How sweet it is,' " Joseph Alioto, the Raiders' attorney, said in a telephone interview last night. "Competition will set the location of where the teams will be playing, instead of planning at 410 Park Avenue the address of NFL headquarters in New York City ."

Judge Harry Pregerson set Sept. 20 as the date for the trial to decide damages. The same jury of six women will hear this part of the case, also. The Raiders had sued for $160 million, the Coliseum Board for $53 million. Under antitrust laws, awards for damages are automatically trebled.

The first proceeding ended in a mistrial last August with the jury unable to reach a unanimous verdict. At that time, the vote favored the Raiders, 8 to 2.

Lynch was critical that an attempt was made to exclude sports fans as potential jurors in both trials.

"We were trying the case in Los Angeles and we were denied jurors who are sports fans," Lynch complained. "We couldn't get a representative jury--and that's not because they are women."

Under orders from the judge, the jurors could not be interviewed because they must return for the damage phase of the trial.

Davis said the NFL will not suffer because it lost the case.

"For 15 years we've known that rule was illegal," Davis said, "and knocking it down like this won't hurt the NFL one bit. We'll still be a great league, but now our laws will conform to the laws of the United States."

Outside the courthouse, Rozelle said, "We certainly lost this round; we'll see what happens in the future."

In a telephone interview last night, Rozelle said, "We'll be working this weekend on an appeal and stay that would cause them to be forced to stay in Oakland. How long it takes will depend on the court."

Asked whether the decision would be appealed to the Supreme Court, Rozelle said, "That's our current plan. We don't think the antitrust laws were intended to face situations where you've had 12 straight years of sellouts and that community is allowed to lose its franchise.

"If so, every franchise would be up for bids. If the Redskins were to move to Jacksonville tomorrow, we'd get real quick action from Congress in that situation."

In a prepared statement issued earlier by the NFL, Rozelle also said he was concerned with the effect the verdict might have on "the basic structure and stability of the National Football League."

Rozelle said, "If the jury's verdict and related rulings of the court are sustained, sports leagues will have been told that league objectives and community commitments are of no legal consequence in antitrust cases. The long-range effects could include a serious erosion of the competitive balance that makes sports entertaining."

The Raiders took the first step back into court after yesterday's verdict when they filed a motion for an injunction, asking the judge to require the NFL to schedule games in Los Angeles if the Raiders decide to move to the Coliseum this season.

Alioto said he expected Pregerson to set a hearing date on that motion Monday or Tuesday.

It appeared that the Raiders will try to play in the Los Angeles Coliseum this season, although Alioto said last night that "business decision" had not been made. He said improvements the Coliseum agreed to make if the team moved to Los Angeles could not be finished in time for the Sept. 12 start of the regular season.

In Washington, Ed Garvey, the executive director of the NFL Players Association, whose group has said it will strike this summer if it cannot reach a new collective bargaining agreement with the league, said he expected that yesterday's verdict in Los Angeles would cause the NFL to intensify efforts to receive an antitrust exemption from Congress. The NFL-NFLPA contract expires in July.

The NFL unsuccessfully lobbied Congress prior to its Easter recess to introduce legislation exempting the league from antitrust laws. The NFL has said the exemption it sought would not cover labor-management issues.

The Los Angeles Coliseum filed the original suit against the NFL in September 1978, after the Los Angeles Rams announced they were moving 35 miles from the city to Anaheim Stadium in Orange County for the 1980 season. In that suit the Coliseum sought an injunction to keep the Rams from moving.

After the Coliseum, a city-owned stadium, lost the bid for an injunction, the Raiders' Davis announced in 1979 that he wanted to move from Oakland Coliseum to the Los Angeles Coliseum for the 1980 season and joined the suit. The city offered to make stadium improvements and put together an $18.5 million package to entice the Raiders.

Al LoCosale, executive assistant to Davis, said Davis decided to move to Los Angeles after concluding that rising salary demands from star athletes would make money extremely important to the success of pro football teams in the 1980s.

However, under Section 4.3 of the NFL constitution, which required three-fourths of the owners to approve the move, the owners voted, 22 to 0, with five abstentions, against Davis.

After a number of legal maneuvers and unsuccessful attempts at reaching an out-of-court settlement, the first trial began last May. Fifty-five days of testimony produced 30 witnesses and more than 10,750 pages of transcript. That jury deliberated 13 days before Pregerson declared a mistrial and ordered the new trial.

There was no immediate reaction concerning possible effects that yesterday's vedict might have on other professional sports. Only baseball is exempt from federal antitrust laws.