DENVER - The spotlight may be focused on Barack Obama this week, but thanks to Hollywood’s long-standing off-screen love affair with politics, he won’t be the biggest star shining.

That may come as a blow to Obama’s critics, who like to mock him as the “world’s biggest celebrity.”

But it’ll be pretty hard to outshine the likes of Chevy Chase, Ben Affleck, Oprah Winfrey, Quentin Tarantino, Sheryl Crow and Daryl Hannah - just a few of the big names expected to make appearances at panels, concerts and fundraisers this week.

Next week in St. Paul and Minneapolis, the Republican National Convention will have its own stars aligning behind their nominee, John McCain - including the Beach Boys, Sammy Hagar, Gretchen Wilson, Charlie Daniels and John Rich, who’s even written a song called “Raisin McCain.”

No matter which party the stars line up behind, Hollywood has a long tradition of using the limelight to promote their favorite candidates. From Charlie Chaplin to Sean Penn, from Al Jolson to Kid Rock, celebrities have never been shy about getting involved in politics.

It’s a romance that runs deep, for reasons that still hold true today.

“The basic idea behind celebrity politics is, in the era before television, in an era where radio was the main source of most information, people weren’t really getting to see and know politicians,” said Steve Ross, chairman of the history department at the University of Southern California, whose book “Hollywood Left and Right: Movie Stars and Politics,” comes out next year. “But they see and know the movie stars, and so the link between celebrity and politics is the same as it’s always been - drawing attention to a candidate.”

The celebs are passionate about their causes, but it doesn’t hurt their exposure, either. Musician will.I.am wrote a song about Obama that has been viewed on You Tube more than 11 million times. Even if that star-studded video wasn’t made with that in mind, it’s a perk.

But celebrities and politicians sharing the stage doesn’t always get rave reviews. Only half of Americans believe stars should get involved at all, according to a CBS/New York Times poll last year.

The same poll showed that 69 percent of Republicans think stars should stay out of it, compared with 33 percent of Democrats - which explains why there appears to be a longer VIP list in Denver than in Minneapolis-St. Paul.

It’s no question that candidates get gigged for their celebrity buddies. In 2004, some critics opined that John Kerry’s cozy relationship with stars made him look like a “limousine liberal” and caused a backlash that cost him the election.

And the McCain campaign has recently made a point of deriding Obama’s popularity with the public and with celebrities.

The idea that stars who spend their days looking good and making TV appearances chafes might actually dare to make a political comment chafes some others on a whole different level.

“Celebrities act, they look pretty and get angry about paparazzi,” read a recent rant on the College On The Record blog, which discusses current events. “Let’s leave the campaigning and trash talking to the politicians, and go back to sunbathing in Saint-Tropez.”

But the criticism, the who-do-they-think-they-are indignation about the perception of Hollywood fluff stepping into the heavy, intellectual arena of politics, can be off the mark in plenty of cases: Charlton Heston, for example, was one of the most effective spokesmen for gun owners in America.

And it doesn’t seem to be stopping them from joining the conversation anyway.

Kal Penn, of “Harold and Kumar” fame, will be telling stories from the campaign trail in a panel alongside actors Kerry Washington, Rosario Dawson and Tatyana Ali.

Musicians James Taylor, Dave Matthews, Randy Newman, Jakob Dylan, and Earth, Wind and Fire, are just a few of the big-name performers scheduled to appear.

Comedians Jon Stewart, David Crosby and Bill Maher - known for their biting political humor - will be here, too.

All of them, said filmmaker David Burstein, deserve a voice in the process. Burstein, producer and director of a youth-vote documentary called “18 in ‘08,” is taping several public service announcements at both conventions to try and get out the youth vote.

“It really frustrates me when people say, ‘Who are they to say anything?’” he said. “I think it’s a good thing, and anybody who’s in a position of influence and prominence in acting, entertainment, sports, or media should use that platform because they’ve got a microphone to make a difference.”

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CELEBRITIES AT THE DEMOCRATIC CONVENTION

Daryl Hannah, Quentin Tarantino, Sheryl Crow, Dave Matthews, Kal Penn, Rosario Dawson, Annette Bening, Stephanie Mills, Boyz II Men, John Larroquette, Spike Lee, Biz Markie, Willie Nelson, Charlize Theron, David Crosby, Ben Affleck, Kerry Washington, will.i.am, Tatyana Ali, Danny Glover, Wilmer Valderrama, Moby, Chevy Chase

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CELEBRITIES AT THE REPUBLICAN CONVENTION

The Beach Boys, Sammy Hagar, Gretchen Wilson, Charlie Daniels, John Rich, Smash Mouth, LeeAnn Rimes, Bellamy Brothers, Jack Ingram, Robert Earl Keen.

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CELEBRITIES AT BOTH CONVENTIONS

Members of the “Creative Coalition” will be at both events. They include Neil Patrick Harris, Susan Sarandon, Maggie Gyllenhaal, Dana Delaney, Rachel Leigh Cook, Matthew Modine.