Celebs stump in Steelton. Camelot comes to King of Prussia. L.A. loves Lock Haven.

Call it what you will, but the stars -- both the political and the Hollywood kind -- have been falling all over Pennsylvania since the Keystone State became a player in this year's presidential primary.

Just this past week, actor/author Hill Harper of "CSI New York" fame was in Pittsburgh to campaign for his Harvard Law School classmate, Sen. Barack Obama.

While Mr. Harper hung out at the University of Pittsburgh student union during Wednesday night's debate, Ethel Kennedy, the widow of Robert F. Kennedy, and her filmmaker daughter, Rory, attended a debate-watching party sponsored by Women for Obama at the Schenley Park Ice Rink. And a week ago, Obama backer Caroline Kennedy was spotted in a King of Prussia coffee shop.

On Sen. Hillary Rodham Clinton's side, her No. 1 A-lister, former president Bill Clinton, has been crisscrossing the state at a furious pace on her behalf. But other celebrity surrogates also have been pitching in, including actor Sean Astin of "Lord of the Rings" and "Rudy," who touted Mrs. Clinton's president-worthy credentials at a number of stops, including Mechanicsburg, Hazleton and Lock Haven.

The actor also appeared with former first daughter Chelsea Clinton earlier this week Downtown and at Carnegie Mellon University. Actress Erika Alexander, best known for her role as Max on the '90s sitcom "Living Single," appeared with Chelsea in Chambersburg. And last month, "Ugly Betty" star America Ferrara stumped for Mrs. Clinton at a union hall in Sinking Spring, Berks County.

The campaigns trot out their star surrogates as if they were playing high-stakes of poker: I'll see your Rob Reiner and raise you a George Clooney. But does all this mega-watt star power make a difference?

"I think celebrities who are well-respected help," said S. Tia Brown, senior editor at the celebrity news magazine, In Touch Weekly. "[People] trust their opinion and they want to feel like they're similar to those celebrities."

She said stars can make voters more receptive to a candidate's message because people are interested in what celebrities' opinions.

But interest does not necessarily translate into votes.

"I don't think there's any evidence that celebrity endorsers or political endorsers make much of a difference in voter behavior," said Martin Kaplan, director of the Norman Lear Center at the University of Southern California and a research professor at the university's Annenberg School of Communication.

"They can have other impacts. They can help with fund raising; they can help build crowds at events. That's especially useful in a state like Pennsylvania, where a certain amount of fatigue might have set in."

Darrell West, a political science professor at Brown University and author of the book "Celebrity Politics," said celebrities are overrated when it comes to elections but agrees that they can garner the media attention candidates crave.

"I think where celebrities have a big impact is with the media. Reporters love celebrities, and the best way to get people to attend your fund-raiser or press conference is to have a big star there," Mr. West said.

Hollywood's fascination with politics and vice-versa is nothing new.

Film legends Mary Pickford, Al Jolson and Douglas Fairbanks threw their silent screen charisma behind Warren G. Harding's presidential bid. Given Mr. Harding's reputation as possibly the worst president in history, they'd probably rethink lending him their star cachet.

John F. Kennedy, with the help of Rat Packers Frank Sinatra, Sammy Davis Jr. and brother-in-law Peter Lawford, gave the presidency a swagger and made it hip to be commander-in-chief.

"In some ways, when we talk about celebrities, it's really a consequence of the age of mass media," Mr. Kaplan said. "There were movie stars before television was predominant who were known as Republican supporters, and the most famous one who comes to mind was Ronald Reagan.

Mr. Reagan traveled the country speaking on behalf of General Electric, and that in turn lead to him speaking at the Republican Convention in 1964. The rest is history.

Sly Stallone is a supporter of Sen. John McCain, the presumptive Republican nominee, but Mr. McCain got more media attention when reality TV star Heidi Montag said she was backing him.

Now, it is the Democrats who seem to be garnering the most A-listers.

"I think part of it is just because a lot of the people who are supporters, who are active in the presidential race are actually activist in other ways," Ms. Brown said. "It seems like those people tend to vote democratically."

Both Mrs. Clinton and Mr. Obama have their share of entertainment heavy-hitters.

Media queen Oprah Winfrey, who can make a book an instant best-seller by mentioning it on her talk show, has thrown her considerable clout behind Mr. Obama. Bruce Springsteen, a hero of the working class, recently released a statement backing the Illinois senator. Elton John held a fund-raiser earlier this month for Mrs. Clinton; Jack Nicholson appeared in a television ad for her

Mr. Obama seems to have a slight edge in attracting young Hollywood stars, including Scarlett Johansson and Nick Cannon, while many of Mrs. Clinton's supporters are among Hollywood's more established stars, such as Barbra Streisand and Stephen Spielberg.

"Sen. Obama is really popular across the board," said Mr. West. "I think Hollywood celebrities are really drawn to his optimism and idealism and hope that things can actually get better."

However, Mr. Kaplan warned, celebrities have to be careful to whom they hitch their star.

Famed actor Ossie Davis' African-American support took a big hit when a photo of him giving President Richard Nixon a playful hug surfaced. Recent reports have linked a downturn in Ms. Winfrey's favorability and the ratings of her perennially popular talk show to her endorsement of Mr. Obama.

"I think there is a risk that celebrities take when they endorse a candidate, especially these days when most choices seem evenly split," he said. "In the end, if you choose one over the other, there's a risk of alienating half of your fan base, so in that case celebrities are rolling the dice."