MoveOn.org is putting its money where its endorsement is.

The anti-war advocacy group that backed Barack Obama in early February is hosting a campaign ad contest for the Illinois senator that will be judged by Hollywood heavyweights. It plans to announce the winning entry right before the pivotal April 22 Pennsylvania primary.

The effort reprises a 2004 contest against President Bush.

The group made a casting call to all Obama girls -- and boys -- on its Web site, asking filmmakers and artists to submit 30-second ads that will be ranked on originality, impact and how effectively they portray Obama's "positive message."

The winning ad from the "Obama in 30 Seconds" contest will be aired on national TV.

"Powered by grassroots enthusiasm, Obama has won the most states and the most delegates. But the race isn't over, and we've got to pull out all the stops to help him across the finish line," says a message on the Web site.

Director Oliver Stone is expected to be one of the contest judges. Also on the panel are musicians John Legend and Moby, actors Steve Buscemi, Matt Damon and Ben Affleck, and music industry mogul Russell Simmons.

MoveOn.org has endorsed Obama and has used its membership network to make phone calls promoting his candidacy and to hold Obama house parties in Texas. By law, the group is not permitted to coordinate its ad campaign with Obama's.

In 2004, MoveOn received 1,500 entries for its "Bush in 30 Seconds" competition. The winner was an ad called "Child's Pay," depicting children performing adult jobs followed by the words: "Guess who's going to pay off President Bush's $1 trillion deficit?" CBS refused to run the ad during the Super Bowl, but it still ended up being among the most watched political commercials, receiving free air time on newscasts and Web sites.

The entries that year, however, included two that compared Bush to Hitler, which MoveOn removed from its contest Web site but which the Republican Party used as examples of "hate speech."

This time, the group was explicit, saying on the entry form that personal attacks will not be accepted.

Click here to view the MoveOn.org casting call.

The Associated Press contributed to this report.