A federal jury in Alexandria gave the government a victory in its legal battle against pornography when it ordered a Lorton couple yesterday to give up business assets, including the contents of 11 stores, because of their racketeering conviction for distributing obscene magazines and videotapes.

Dennis E. and Barbara A. Pryba, convicted Nov. 10 on three counts of racketeering and seven counts of interstate transport of obscene materials, were allowed to keep a $1.9 million house and a 1984 Mercedes-Benz valued at $53,000. The jury found those had not been used to further the aims of the Prybas' racketeering enterprise.

The verdict, reached after nine hours of deliberation, allows the government to close the three adult book stores and eight video shops operated by the Prybas in the Washington area.

Henry E. Hudson, U.S. attorney in Alexandria, whose office prosecuted the case, said the verdict was a victory and estimated the value of the seized assets yesterday at $1 million. The Prybas' defense attorneys, William B. Cummings and Thomas Morris, said the properties are worth about $167,000. After loans on the properties are paid off, the value would fall to about $40,000, the attorneys said.

"If {Hudson} gets 10 percent of {$1 million}, I'll take him to dinner," Cummings said.

Asked about the jury's exclusion of the house and Mercedes-Benz, Hudson replied: "Certainly we would have liked to forfeit more of the assets . . . but I can see where the jury had difficulty seeing where the home and automobile were a direct influence over the business."

"It's certainly a mixed victory for the government," said constitutional specialist Bruce Ennis. "They didn't get the most valuable assets of the defendants. I'm not happy about it because it allows the forfeiture of lawful inventory . . . . In terms of the First Amendment, it's a defeat."

The Prybas must forfeit a $120,000 warehouse in Upper Marlboro, five cars and the contents of the couple's adult book stores and video rental shops, called Video Rental Centers.

In addition to losing those assets, the Prybas each face up to 95 years in prison and maximum criminal fines of $785,000 at their Dec. 18 sentencing.

They are appealing their convictions and the forfeitures, their attorneys said.

The first-of-its-kind prosecution was seen as a trial run for federal prosecutors who have been directed to use racketeering laws against major distributors of obscene materials in order to combat what U.S. Attorney General Edwin Meese III last year called "an explosion of obscenity."

At issue in the trial of the Prybas were four videotapes and nine magazines. The jury found 10 of the items obscene. According to defense attorneys, the retail value of those items was $105.40.

Instructing the jurors before their deliberations on forfeiture, U.S. District Judge T.S. Ellis III said they should determine if any of the couples' assets fit any one of three criteria: If the asset afforded "the defendants a source of influence or control" over the racketeering activity (in this case, dealing in obscene materials).

If it "derived from any proceeds" of the illegal activity.

If it was "acquired or maintained" from profits of the racketeering activity.

In the last two categories, Ellis said the jury had to find that the rofits "provided a substantial or signficant part of" the money used to acquire or maintain the property.

Defense attorneys Cummings and Morris said they believed that this swayed the jury to rule out forfeiture of the house and car. They had argued to the jury that the $105.40 in proceeds from the obscene tapes and magazines was not enough to cover expenses on the two properties.

The jury must assume, said Cummings, that the rest of the Prybas' income came from the sale or rental of materials not found obscene, and thus carried the free speech protection of the First Amendment. Both sides in the case acknowledged that the Prybas' video shops also rented general-audience films.

Prosecutors Cynthia Christfield and Lawrence J. Leiser argued that the Prybas earned more than $105 from the obscene materials because they had rented copies of the videotapes many times over several years.

As for the seven-acre family estate, Christfield said, it was "basically Barbara Pryba's satellite base of operations." Here, she telephoned employes, counted quarters from "peep machines" in the adult book stores and kept $9,000 in cash, the prosecutor said.