''This is incredible,'' said Paul Dergarabedian, president of the Exhibitor Relations Company, which monitors the box office for theater owners. ''We've never heard of a trailer packing people into a theater. It's a precedent-setting event.'' He said the reaction to the gimmick made it inevitable that the new ''Star Wars'' would have powerful audience appeal. ''It's going to reach fever pitch with this movie, which is unquestionably going to be one of the biggest of 1999,'' Mr. Dergarabedian said

Tom Sherak, the chairman of Fox's Domestic Film Group, said the idea for the early-in-the-week trailer, which was released nationally over the weekend, came from Mr. Lucas's associates. ''They said since they have such a big fan base, why not set something up just for the fans first and make sure it's shown to the rest of the public very quickly?'' he said. ''The idea was to figure out a way to have fun with this. 'Star Wars' is part of the culture, but it's still a movie. Let's treat it like a movie.''

Underscoring the box office impact of the trailer -- and the trailer alone -- were the substantial gains made on Tuesday night over Monday at theaters showing it. At the Mann Theater in the Westwood section of Los Angeles, near the University of California, ''The Siege'' took in $13,000 on Tuesday night; it had taken in only $1,000 on Monday night. At the Union Square Theater 14 in Manhattan, ''Meet Joe Black'' grossed $6,300 on Monday night, but $10,800 on Tuesday night.

The new ''Star Wars'' is the first of three planned prequels that will go back in time a full generation and detail the story of Anakin Skywalker's transformation into the mysterious and sinister Darth Vader. In the new film, Skywalker is a 9-year-old boy and Obi-Wan Kenobi is a brash young Jedi knight.

Mr. Lucas himself has virtually total control over the film. Not only has he put his personal fortune into it, he is in charge of its promotion and distribution. No decisions are made without his approval.