WASHINGTON — It makes sense for Barack Obama to slug it out with Jerome Corsi, whose new book paints the presumptive Democratic nominee as a dangerous radical, analysts said Friday.

But Obama's strategy also carries some risks.

"The old saying is that when you get in the gutter, everybody gets dirty," said Kevin Wagner, an assistant professor of political science at Florida Atlantic University, particularly with information flying across the Internet.

Corsi's book, "Obama Nation: Leftist Politics and the Cult of Personality," is number one on The New York Times hardcover nonfiction bestseller list. The Obama camp responded Thursday with a 41-page, point-by-point refutation of the key charges.

Tobe Berkovitz, associate dean of the Boston University School of Communication, sees the rebuttal as a smart move.

"The average citizen won't go through all 40 pages," he said, "but it's important for Obama to portray Corsi as a demented right-wing loon."

Corsi is well-known in political circles. Four years ago, he co-wrote with John O'Neill, co-founder of Swift Boat Veterans for Truth, the book "Unfit for Command," which raised questions about Democratic presidential nominee John Kerry's military record.

Corsi, who earned a Ph.D. from Harvard University in political science, has said he plans to vote this year for Chuck Baldwin, the Constitution Party's presidential candidate.

He argues in his book that Obama's election would mean "a repeat of the failed extremist policies" that have dominated the Democratic Party for years.

To critics, such arguments are reminiscent of Corsi's 2004 assertions about Kerry, a decorated Vietnam veteran. The senator responded to charges in the book and by the Swift Boat Veterans for Truth, but his reply was widely criticized as being too academic and low-key.

Obama's camp tried to show that it had learned that lesson this week with its lengthy refutation, which it called "Unfit for Publication."

Perhaps just as significantly, spokesman Tommy Vietor slammed Corsi, calling him "a discredited liar who is peddling another piece of garbage in order to continue the Bush-Cheney politics he helped perpetuate four years ago."

Corsi explained this week on CNN that "the book is designed to say that I oppose the candidacy of Barack Obama, and I explain why. I've got 360 pages and nearly 700 footnotes explaining my argumentation about Obama (and a) complete examination of his life, his positions, his background."

Corsi couldn't be reached for comment Friday.

Berkovitz said there generally were two ways to respond to such charges.

One method, used by Kerry and in 1988 by Democratic nominee Michael Dukakis, is to take a higher road.

"You say, 'How can anyone impugn my reputation like this? The American people are too smart to believe this stuff,' " Berkovitz said.

Republicans attacked Dukakis for supporting a prison furlough system that allowed convicted murderer Willie Horton to be released. Horton later stabbed a man and raped and tortured his girlfriend.

The other way to confront what seem like wild allegations, credited most recently to Bill Clinton in the 1990s, is to respond early, fiercely and often. The problem with such aggressive responses is that they risk keeping the story alive.

"Reminding people of negative information isn't usually helpful. You can give credibility to it even though you're saying it's wrong," said Susan Sterett, a professor of political science at the University of Denver.

Some argued that Obama's case is somewhat unique, because he's spent much of his presidential campaign battling rumors about his background.

"There continues to be this mystery about him," said John Straayer, a professor of political science at Colorado State University.

Rivals routinely paint Obama as an elitist, for instance, when "he's an African-American who raised himself up by his bootstraps, the real American dream," Straayer said.

The incorrect perceptions persist, however. A July survey by the Pew Research Center found that 12 percent of voters thought that Obama was Muslim, up slightly from 10 percent in March. Another one-fourth of voters said they didn't know Obama's religious beliefs.

That's another reason that Obama has to fight back, Wagner said. "This election is a referendum on Obama," he argued. "The correct play for him is to look like he's a fighter."

ON THE WEB

The Pew survey of views of Obama's religious beliefs

The New York Times bestseller list

Obama's statement

A transcript of Corsi's interview on CNN