The Supreme Court boosted the federal government's crackdown on obscenity Monday as it let stand the forced closing of three adult bookstores and nine video rental shops in Virginia.

The court, over one dissenting vote, rejected arguments by the businesses' owners, who were convicted of racketeering and selling obscene materials, that the subsequent seizures of the businesses violated their free-speech rights.Justice Byron R. White voted to hear arguments in the case, but four votes are needed to grant such review.

In other decisions Monday:

-The court, which has twice ruled that burning the American flag is protected political speech, set aside a Minnesota man's flag-burning conviction. The justices told a federal appeals court to restudy a free-speech challenge to the man's federal conviction for burning the flag.

-Ruled against a former Air Force sergeant convicted of aggravated assault because he engaged in homosexual conduct while knowingly infected with an AIDS-related virus. The justices let stand the man's conviction, dishonorable military discharge and six-year prison sentence.

-Refused to revive a copyright lawsuit over an unauthorized biography of L. Ron Hubbard, founder of the Scientology religion. The justices, without comment, let stand a decision throwing out allegations of copyright infringement against the book's publisher.

-Refused to help states ban deceptive advertising by airlines.