A new book scheduled to hit stores as early as this week poses a challenge to John Kerry's (search) version of his military record in Vietnam, but Kerry supporters say the book is a product of the Republican Party's "extreme wing."

"Unfit for Command" (search), scheduled for release on Sunday, accuses the Democratic presidential nominee of lying about his decorated wartime record and betraying comrades by returning from Vietnam and alleging widespread atrocities by U.S. troops.

And in a year in which the publishing world has been bombarded with politically-geared books — mostly anti-Bush material — this book may stand out from the masses. It is already No. 1 on Amazon.com's best-seller list.

"Unfit for Command" claims that Kerry earned his Silver Star not in a barrage of enemy fire, but rather by killing a fleeing Viet Cong teenager. It also questions the three Purple Hearts Kerry earned, saying none was for serious injuries and two wounds were self-inflicted.

According to medical records from his naval service, Kerry still has shrapnel in his thigh from a war injury.

The book's co-author, John O'Neill (search), succeeded Kerry in command of a swift boat and is spokesman for Swift Boat Veterans for Truth (search), which began airing an anti-Kerry ad last week.

O'Neill faced off against Kerry more than 30 years ago on "The Dick Cavett Show" to debate the Vietnam War and to challenge Kerry's assertions of atrocities being committed. O'Neill claims there were no atrocities committed by him or by swift boat sailors like Kerry.

"We would have died rather than kill someone who was innocent," O'Neill told "Fox and Friends" on Wednesday.

O'Neill says "Unfit for Duty" includes many people who served in adjoining swift boats or who commanded Kerry, all disputing the Massachusetts senator's version of events.

According to many of these people, for example, Kerry's story about saving former Special Forces officer Jim Rassmann (search) in 1969 is wrong and "a total lie," O'Neill said.

Kerry, Rassmann and other crewmen say Rassmann was knocked from the deck of Kerry's patrol boat during an ambush on March 13, 1969. When he came up for air, the boat was gone and Viet Cong were sniping at him. Kerry turned the boat around and came back for Rassmann and pulled him into the boat, earning a Bronze Star for valor and a Purple Heart for being wounded that day.

Rassmann has been stumping for Kerry for months, telling his story to Kerry supporters. He was even a speaker at the Democratic National Convention in Boston.

O'Neill and others in the book say Kerry injured himself in Vietnam, which should have prevented him from getting his first Purple Heart. After his first injury, the commander turned Kerry down, so he waited until the commander was gone and applied again — and received — the medal, the book claims.

A Right-Wing Campaign?

Jeh Johnson, a former Air Force general counsel and informal adviser to Kerry, disputed these claims, saying they're simply part of a smear campaign.

"The American people recognize this is an effort financed by the right wing, the extreme wing of the Republican Party," Johnson told "Fox and Friends" on Wednesday.

Johnson noted that even former Arizona Sen. John McCain (search), a Republican and former Vietnam POW, and various editorial pages have condemned the book and have called on the GOP to renounce it.

Johnson disputed many of the points in "Unfit for Command," arguing that Kerry did in fact save Rassmann and has authorized the release of records related to his military career to prove his claims.

The Cambodia Question

What Kerry did and where he spent time in and around Vietnam have also come into question.

"Unfit for Command" raises questions about the Boston Brahmin's past claims that he was in Cambodia on Christmas Eve 1968; the U.S. government claims there was no American military presence in that country then.

Kerry has said that he was close to the Cambodian border that day, being shot at by South Vietnamese allies who were drunk and celebrating Christmas.

"It's a total and complete lie. It's a total fabrication," O'Neill told FOX News. "He's said it 50 times and yet in his new book, he's in a base in Vietnam dreaming of sugar plums."

Kerry has said on the record that he was mistaken in his recollections and has since said he was on a river near Cambodia, not actually in the country.

"He chose to risk his life for his country and his fellow crew officers. That's the man we need to be commander in chief," Johnson said.

O'Neill said he had been asked many times over the past 30 years to be aggressive in going after Kerry, but he had declined until now. And he says he's not deterred by those who have filed a lawsuit trying to stop him.

"We have a right to talk about it ... it's a sad book for a lot of us," O'Neill said.

In Kerry's defense, Johnson said "Unfit for Command" is not based on interviews with people who knew Kerry the best. Rather, the book quotes other swift boat captains and some of Kerry's commanders.

"There are no first-hand accounts, all second, third-hand accounts," the Kerry adviser said.

FOX News' Liza Porteus and The Associated Press contributed to this report.