A corporation that owns a Fairfax County adult bookstore was convicted of selling obscene magazines and fined $6,000 yesterday following one of the county's few successful magazine obscenity prosecutions.

A Fairfax Circuit Court jury of six women and six men deliberated about two hours before finding Croatan Books, Inc., 8653 Richmond Hwy., guilty of selling six obscene publications. Judge Barnard F. Jennings then imposed the fine the jurors agreed on.

Prosecutors said they believe the outcome to be one of the few such convictions in Virginia as well as the counties since the U.S. Supreme Court ruled in 1957 that obscenity must be determined by applying local community standards.

Thaddeus P. Mikulsky, the assistant Fairfax commonwealth's attorney who prosecuted the case, said the county plans to increase prosecutions for selling obscene materials.

The owner of the store was not present at the trial and could not be reached for comment.

The store's attorney, Steve H. Glickman, said he tried to convince the jury that the six magazines were no more offensive than "Hustler," "Velvet" and similar magazines sold in local drugstores.

Mikulsky said the six magazines had pictures of sadomasochism and other practices and added, "I think the jury decided that these items fall outside the protection of the First Amendment in Fairfax County."