Like "Wag the Dog," "Primary Colors" is a political satire striving to be so realistic that it almost seems ripped from today's headlines. Unlike that film, though, "Primary Colors" doesn't know when to quit while it's ahead.

This dark comic drama, based on the best-selling novel by Anonymous, starts out promisingly enough, and the first half is pretty funny and well-paced. But in the second half the story becomes so downbeat and preachy that the movie feels much longer than its 143 minutes."Primary Colors" also differs from "Wag the Dog" because it actually lets us see the embattled president at the center of the story, who is obviously based on our current commander-in-chief. Despite the fact that the character is played by John Travolta, that's a big mistake.

While Travolta has painstakingly tried to duplicate President Clinton's Southern drawl, his performance seems more like a lengthy impersonation than real acting, and the movie suffers for it.

To its credit, much of the story early on is about Henry Burton (newcomer Adrian Lester), a former political aide with some mighty big shoes to fill. The grandson of one of the country's most prominent black activists, Henry is looking for a candidate and campaign to believe in.

And he thinks he's found his man in Jack Stanton (Travolta), a suave Southern governor running for president as a Democrat. Jack and his politically savvy wife, Susan (Emma Thompson), quickly convince Henry to join Team Stanton, which also includes redneck strategist Richard (Billy Bob Thornton), campaign trouble-shooter Libby (Kathy Bates) and media adviser Daisy (Maura Tierney).

But they've got a hard fight on their hands, especially in the primary elections, where shady bits of Jack's past keep surfacing, including evidence of an affair. Still, that's nothing compared with the threat of Fred Picker (Larry Hagman), a retired politician who steps in for another candidate, and who becomes the front-runner.

That puts Libby and Henry in the uncomfortable position of trying to dig up dirt on Picker, which makes Henry reconsider his political and personal beliefs.

Subtlety isn't director Mike Nichols' strong point this time around. Instead, he and screenwriter Elaine May load down the movie with cheap jokes obviously aimed at the president (particularly his eating habits) and heavy-handed political statements wielded with clublike bluntness.

And as mentioned, Travolta concentrates so much on his Clinton affectations that he forgets he's supposed to be acting.

More's the pity, because the rest of the cast really tries. Lester is particularly good, although his natural British accent keeps resurfacing. Also, Thornton nearly keeps the film afloat single-handedly (until his character disappears midway through the pic-ture) and Thompson again proves how adept she is at comedy.

"Primary Colors" is rated R for profanity, vulgar jokes and references, violent slapping, racial epithets and brief, partial female nudity.