After successfully prosecuting the only two adult book stores in Fairfax County, the county prosecutor's office turned its sights yesterday on a new target: home video cassette rental stores.

Assistant Commonwealth's Attorney William Minor was in the county's General District Court yesterday prosecuting the Video Rental Center, 9156 Richmond Hwy., on a single misdemeanor count of renting obscene material.

It was the first time the Fairfax prosecutor's office -- known state-wide for its success in prosecuting obscenity cases against the two book stores -- has prosecuted a video cassette rental store, but Minor said it will not be the last.

Video Rental Center is a chain of stores with outlets in Alexandria, Rockville and Oxon Hill, as well as Fairfax County. Like most video rental outlets, the store stocks a range of movies, including some that have G ratings.

Substitute General District Court Judge Gus Watson, after viewing a portion of the movie in question, which depicts sexual acts in explicit detail, and hearing testimony and argument, said in court, "I think you're basically guilty, but I'm willing to hear argument on a technical defense."

The store's attorney, Thomas J. Morris, agreed that the film "violates the community standard of obscenity," but contended that store officials did not know its contents, as they must in order to be convicted.

Watson said he will rule in the case in about 10 days after receiving briefs from Morris and Minor.

Morris was unsuccessful in defending the adult bookstores against charges of distributing obscene material.

Minor said one of the stores has gone out of business, and the other "may well" go out of business when it is forced to pay more than $80,000 in fines.

Minor said the point of prosecuting the video stores was that "the video store owners -- just like the movie theater owners and the bookstore owners -- are to comply with the obscenity laws." There apparently are no theaters in the county at present that show exclusively X-rated movies.

Minor and other prosecutors said many video rental stores avoid the potential of facing obscenity charges by not stocking X-rated material.

The first conviction for distribution of obscene materials is a misdemeanor with a fine of up to $1,000. All subsequent convictions are felony convictions punishable by fines up to $10,000.

Arlington Commonwealth's Attorney Henry Hudson said his office had successfully prosecuted "one or two" video rental stores recently. "We routinely follow-up complaints of obscene materials," Hudson said, "and as part of that we routinely check up on the video stores."