IF AT FIRST . . . IF AT SECOND . . .

Warner Bros. is taking another shot with “Innerspace,” its surprise Steven Spielberg-produced dud of last summer.

The Dennis Quaid-Martin Short comedy-adventure wasn’t due to surface again until a spring home-vid release. But Warners, armed with a new ad campaign, has decided on a “reissue” this weekend in Boston, Cincinnati, San Antonio and Tucson.

“We want to see if it has more life in it in a less competitive environment,” a Warners spokesman explained. “It’ll probably take at least two weeks for us to really analyze how it’s doing.” The spokesman confirmed that Warners “did modify the ad campaign,” but refused to discuss its old ad or describe its new one.

That’s OK. We found a friendly display-ad salesman at the Arizona Daily Star: “The ad has a picture of a guy with big eyes and his mouth wide open (presumably Short) who has a strange-looking spaceship flying out of it, with this other guy (Quaid) looking out the windshield.”

The new copy: “A Huge Dose of Comedy in One Big Gulp. ‘Inner’s’ Out Again . . . For the Millions Who Are Going to Love It!”

And don’t worry--credits are introduced with “Steven Spielberg Presents” in large print.

We’re dying to know what Quaid thinks of this new attack. His opinion of Warners’ original campaign? “They really screwed it up,” he told a Chicago reporter recently. “They made it look like a space-hardware adventure instead of a human comedy.”