In the first case of its kind, three Fairfax County residents have been indicted under federal racketeering laws for distribution of allegedly obscene materials through a chain of adult book and video shops in the Washington area.

Authorities said the precedent-setting use of racketeering statutes could enable them to impose stiffer penalties on vendors of pornography by seizing all property and revenue gained through the distribution of the materials.

Dennis E. Pryba and his wife, Barbara A., of Lorton, and Jennifer G. Williams of Woodbridge, Barbara Pryba's sister, were charged with 12 counts of violating federal organized crime statutes. The indictments were unsealed yesterday.

U.S. Attorney Henry E. Hudson, who sought the indictments, said that by using the Racketeer Influenced and Corrupt Organizations Act, prosecutors can greatly increase the pressure on people charged with distributing obscene materials.

Hudson, who served as chairman of the Presidential Commission on Pornography in 1985, described the case as a landmark.

"It certainly will have an effect on prosecutions of these types of cases elsewhere in the United States," he said.

Barry Lynn, a spokesman for the American Civil Liberties Union, said the indictments would have "a chilling effect" on free speech rights guaranteed by the Constitution.

"They are trying to put every pressure they can on people who are involved in what we must presume to be a constitutional activity," Lynn said. "You have significant First Amendment implications here."

If convicted, the Prybas and Williams could be forced to forfeit any earnings from the trafficking of pornography. Hudson's office is attempting to seize the contents of 11 book or video outlets, a warehouse, cars, bank accounts and a Lorton house described as "a $2 million estate."

Attorneys for Barbara Pryba and Jennifer Williams said yesterday they had not had time to review the charges against their clients, but that their clients would contest the allegations.

Neither Dennis Pryba nor his attorney could be reached for comment.

All three are scheduled to be arraigned in U.S. District Court in Alexandria on Monday.

The indictment charges that since 1973, the Prybas and Williams have operated a chain of book and video stores that distributed allegedly obscene materials, and that their business activities formed "a pattern of racketeering activity."

According to the indictment, the three set up a chain of interlocking corporations to operate the businesses in Virginia and Maryland. The video shops operated under the name Video Rental Center. One of the business entities that sold magazines and videos was called Educational Books Inc.

Since 1981, according to the indictment, Educational Books outlets in Fairfax County have been convicted 15 times for violating Virginia obscenity laws. The indictment also cites 10 other occasions since December 1985 when Educational Books or Video Rental Center outlets either sold or rented allegedly obscene material.

Ten of the 12 counts of the indictment charge the Prybas and Williams either with distributing obscene material or with transporting obscene material across state lines. The remaining two counts charge Dennis and Barbara Pryba with tax evasion, contending that during 1984 and 1985 they failed to report about $300 a week in income from the various businesses.

As part of the charges, the indictment also alleges that the Prybas and Williams have attempted to hide their involvement with the book and video stores.

According to the indictment, Dennis Pryba is the principal owner of the business, while Barbara Pryba and Williams help manage its affairs. The indictment charges that the Prybas attempted to "recruit false corporate officers and directors as part of a scheme and artifice to hide the true identities of the actual officers."

To win a conviction under federal racketeering laws, prosecutors must prove that the material distributed by the businesses is obscene, that the businesses have an ongoing involvement with obscene material and that the Prybas and Williams operate the businesses.

The power to close down the stores through financial pressure is a criticial distinction between the federal racketeering laws and Virginia's obscenity statutes. Despite repeated convictions under state statutes, Educational Books remains in business.

Hudson said Fairfax County officials requested the federal probe after they were unable to take stronger action against Educational Books.