The giant Blockbuster Video chain has struck a sharp blow to the new NC-17 movie rating by announcing that it will not stock any movie that carries the adults-only designation.

The move by the 1,600-outlet Blockbuster, America's largest video retailer, was the clearest sign yet of a growing perception that NC-17 equals the X rating that it replaced.

"We have always had a policy that we don't carry any movie that the Motion Picture Association of America rates X," Blockbuster spokesman Ron Castell said Friday from the company's Florida headquarters.

"When they revised the X rating, we said we would wait and see how they would use the new rating. But the criteria used for NC-17 was the same as the X," Castell said.

"So we're saying that since NC-17 is the same criteria as the X, we're not going to carry it."

Many theater chains, video stores and newspapers previously have announced they would judge NC-17 rated movies on a case-by-case basis before booking, stocking or running ads for films with that rating. Blockbuster's decision is one of the first that categorically bar all movies with the NC-17 rating.

The NC-17 rating was introduced by the MPAA in September in hopes of ridding the rating system of the stigma of the X rating, which was generally regarded as synonymous with pornography. The new rating was copyrighted by the MPAA so that it could be used only by films that were officially rated. Most low-budget pornographic films are not submitted to the ratings board.

Castell said Blockbuster Video's decisionhad no connection to a boycott recently begun by the Tupelo, Miss.-based American Family Association and its crusading family-values leader, the Rev. Donald Wildmon. Blockbuster, Castell said, had received "less than a thousand" preprinted postcards from members of Wildmon's group that said they would "take their business to another video store until you stop carrying NC-17." But after phoning some senders of the cards, Castell said, "we found that most came from people who don't do business with us anyway."