A six-person jury today found the National Football League liable for one antitrust violation, but ordered the league to pay only one dollar in damages to the rival United States Football League, which had sought $1.69 billion.

In a stunning blow to the USFL, the jury found that the NFL used monopoly power to damage the younger league and to retain control of the professional football market, but determined that the damage incurred by the USFL was virtually nonexistent.

The jury cleared the NFL on all eight other charges, including the key charge of the case -- that the NFL had denied the USFL access to a network television contract. Commissioner Pete Rozelle of the NFL also was found not liable by the jury, which consisted of five women and one man.

Since all damage awards in an antitrust suit are trebled, the NFL owes the three-year-old USFL $3. "A clean sweep," Rozelle said today. "All the jury said was what I had testified: that we are a natural monopoly. In my view, all professional sports leagues are that and have been since before the turn of the century. Now we can go back to playing football."

The USFL, which has been unable to secure a network television contract since it moved from a spring schedule to the fall, alleged that the NFL illegally "tied up" the three networks in violation of the Sherman Antitrust Act. Besides damages, the USFL sought injunctive relief to force the NFL to give up its contract with at least one network. Judge Peter K. Leisure presided over the trial.

The verdict, reached after 31 hours of deliberation over five days, could be the death knell for the USFL. Its commissioner, Harry Usher, said outside Room 318 of U.S. District Court at Foley Square today that the club owners would meet Aug. 6 to "determine what this decision means." It was unclear if the USFL will appeal.

Before the trial, Usher had said the USFL would play this fall regardless of the outcome. During the trial, however, New Jersey Generals owner Donald Trump testified that the league's future was "dependent upon the outcome of this trial," and USFL lead counsel Harvey Myerson said that without the award of at least $301 million in damages (the minimum sought by the USFL), "the league is dead."

Usher said today, "It's a confused state. It's difficult to reconcile the finding that the NFL acted in a monopolistic, predatory fashion but that we weren't damaged except to the extent of $1."

Myerson added, " The jurors have given a monopolist who has been proven to be a monopolist a license to continue being a monopolist."

Reached at his Northern Virginia home, Washington Redskins owner Jack Kent Cooke said, "I'd like to be the one to present the USFL with three crisp $1 bills. I can afford it.

" . . . By golly, it's great that we can count on the basic common sense of the American citizen. This is great intelligence mixed with a marvelously humorous jot of wit. I never had a doubt that we would win."

One juror, Margaret Lilienfeld, a retiree who lives in Shenorock, N.Y., said, "We decided that there was a monopoly and that the NFL had tried to maintain it, but the USFL had damaged themselves."

Another juror, Miriam Sanchez, a high school English teacher from Yonkers, N.Y., who described herself late today as the staunchest USFL supporter among the six jurors, said the jury was equally divided at the outset of deliberations. Sanchez said, "I never scream, and I was screaming all over the place. . . . I definitely feel the NFL was responsible for the USFL's downfall. Everybody should have their chance to get their foot in the door in this country."

Sanchez said she felt the USFL was entitled to between $200 million and $300 million in damages, but said she eventually consented to award only $1 because she believed a large-damages award would have been reduced by the judge. Sanchez said she felt the judge, at his discretion, could increase the amount of a small-damages award.

A USFL spokesman said later, "It appears from the jurors' statements that there were possible errors which led to a confused result on damages. These matters will be brought to the attention of the court."

The case was opened at 4:48 p.m. on Oct. 17, 1984, when a law-firm clerk filed the USFL's 39-page complaint for the standard $60 filing fee. The complaint was signed by two USFL attorneys, including Roy Cohn, onetime counsel for the late Sen. Joseph McCarthy. (Cohn later relinquished his role in the case, apparently for health reasons, and most recently was disbarred.)

The filing of the complaint and the announcement of the jury's verdict today were separated by more than 21 months, a total of 44 witnesses over 49 trial days, between $9 million and $14 million in legal fees, according to sources, and 6,551 transcript pages.

In a pretrial opinion, Leisure wrote that, "Television is at the heart of this case." At the least, the trial provided great insight into how the television dollar fuels the professional football industry.

The USFL's offense was, in essence, a three-pronged charge:

That the NFL illegally "tied up" the three television networks, putting all three "in the loop" by rotating Super Bowl telecasts, and subtly pressured and coerced the networks not to televise USFL games in the fall of 1986.

That NFL officials engaged in anticompetitive behavior in conspiring to keep USFL teams out of New York and Oakland.

That the NFL commissioned a 1984 presentation by Michael Porter, a Harvard Business School professor, which Myerson termed the "How to Conquer the USFL" seminar, then implemented Porter's recommendations such as co-opting USFL owners with promises of future NFL franchises and dissuading ABC from televising USFL games.

The go-for-the-throat approach of Myerson was a crucial element in the USFL's trial strategy. After being examined for five days by Myerson, Rozelle said, "I feel like a hostage being let go."

Some of the most vital USFL testimony was given by Usher, Trump, sportscaster Howard Cosell and the Los Angeles Raiders' Al Davis, the only NFL owner not named as a defendant.

Usher testified the NFL "bashed and bludgeoned" the USFL and, consequently, "we are dying." Trump testified that, in a 1984 meeting with Rozelle in Manhattan, Rozelle offered him an NFL franchise in exchange for dropping the suit (a statement Rozelle denied). Davis testified that the NFL, the Oakland-Alameda County Coliseum and Oakland city officials formed an "illegal collaboration" to stifle the USFL's Oakland Invaders. (Davis went through his own -- successful -- litigation in 1981 against Rozelle and the NFL over his Raiders' move out of Oakland.)

Cosell contradicted his former boss, former ABC Sports chief Roone Arledge, when he testified that Arledge told him Rozelle "was all over me" for televising USFL games.

The heart of the NFL's defense involved executives from ABC, CBS, NBC and ESPN, a cable network that specializes in sports programming, all of whom testified that the NFL did not exert any pressure on them in regard to the USFL. Also, the NFL alleged that the USFL brought about its own troubles by mismanagement and moved to the fall as part of Trump's "grand plan" for a merger with the NFL.

Furthermore, the NFL maintained that the "NFL vs. USFL" presentation by Porter of the Harvard Business School to 65 NFL executives was given without prior knowledge of the NFL and was not, in any way, implemented.

Finally, New York Jets owner Leon Hess contradicted Davis regarding the so-called "New York Conspiracy," in which the USFL alleged that Hess and the NFL misled New York government officials into believing the Jets would soon return from nearby New Jersey to New York City so as to keep a USFL team out of the nation's No. 1 television market. Hess testified the city simply didn't provide him with adequate plans for a new stadium.

The trial was full of contradictions. One economist, testifying on behalf of the USFL, said the USFL was due between $301 million and $565 million in damages. However, an economist testifying on behalf of the NFL said the methods of analysis used in determining damages had been improper and that the USFL was due "negative damages," which is to say, zero damages.

After the verdict was announced, Leisure thanked jurors, telling them, "You have decided a complicated case."