MR. SLATER WAS HEADED TO Sunny L.A., but he had to take a little detour." The speaker was D. Joy Faber, a spokeswoman with the Port Authority of New York, which runs the police force at Kennedy International Airport. The subject was the 8 hours Christian Slater spent in a holding cell two nights before Christmas.

The 25-year-old star Interview with the Vampire allegedly committed his crime in the boarding area of MGM Grand, the all-first-class airline he was planning to take home for the holidays. Slater was there to catch a 6:30 p.m. flight to L.A. from New York City, where he had just finished shooting Amelia and the King of Plants, a romantic tale costarring Mary Stuart Masterston. A security official, examining Slater's black nylon carry-on bag through the screening machine, discovered a 6.5 mm. Beretta handgun and six rounds of ammunition. Worse, the gun was unregistered, and Slater didn't have the required federal permit to travel with it interstate. He was promptly arrested and spent the night with other prisoners at the Queens Criminal Court. The following morning, before being released on his own recognizance, he was arraigned on a charge of criminal possession of a weapon in the third degree. That's a federal offense and a big worry for Slater, who's already on five years' probation for a 1990 drunk-driving incident in Los Angeles. Carrying a weapon constitutes a violation of probation, regardless of state.

Motive? Don't ask the authorities. "I scratch my head when celebrities try to bring firearms through the airport," says Faber, alluding to singer Harry Connick Jr.'s arrest for the same offense at the same airport two years ago. "Maybe they think they have immunity." Christian wasn't talking, but his mom, casting agent Mary Jo Slater, spoke with her son briefly and, she says, "I guess he feels he needs the protection."

The police luggage inspection did reportedly turn up one happier clue about Slater's state of mind. Port Authority's Faber says she heard that Slater was "in possession of an engagement ring"—possibly for Nina Peterson Huang, 27, the actress he lives with in the Hollywood Hills. Indeed, says one source from the Amelia set, "There'd been a rumor that they were getting married." And, says Faber, the word was that "Slater's attorney said, 'He's trying to get engaged. Be a little lenient.' " Good try—but Slater is due back in court for a hearing on Jan. 27.