* Pentagon reviewing copy of book by former commando

* Publication of book moved to September 4

WASHINGTON - A US Navy SEAL who has authored a first-hand account of the raid that killed Osama bin Laden says the al-Qaeda leader was shot in the head as he peeked from a bedroom door, an account that diverges from the Obama administration's orig inal desc ription of the incident.

The book, "No Easy Day," due to be published September 4, says bin Laden was unarmed when Navy SEALs found him during the raid on his Pakistan compound, according to a source who read the book, which is due to be released on September 4.

The book's author, writing under the pseudonym "Mark Owen," says bin Laden was looking out from his bedroom door when he was shot in the head, said the source, who spoke on condition of anonymity.

In the confused hours after the raid, White House counter-terrorism adviser John Brennan had originally said that bin Laden "was engaged in a firefight" with the Navy SEALs.

The White House amended that account a day later, saying he was not armed but had resisted capture inside an upper-floor bedroom in the compound.

National Security Council spokesman Tommy Vietor declined comment on the book.

"As President Obama said on the night that justice was brought to Osama bin Laden, 'We give thanks for the men who carried out this operation, for they exemplify the professionalism, patriotism, and unparalleled courage of those who serve our country,'" Vietor said.

Colonel Tim Nye, spokesman for the Pentagon's Special Operations Command (SOCOM), said that he and other Defense Department officials received copies of the book late last week from the publisher, Dutton.

US officials said last week they were surprised by the book, which was not vetted by government agencies to ensure that no secrets were revealed.

Pentagon officials now are reviewing its contents to see if it contains classified information and to determine if further steps can or should be taken against the author, who should have submitted the book for pre-publication review under the terms of his service in the Navy SEALs, Nye said.

Two sources familiar with official US government reporting on the bin Laden raid said it was unsurprising that there were discrepancies between the book's account of how bin Laden was killed and previous official versions.

In any combat situation, participants in the operation would normally come away with different accounts and perceptions of what happened, the sources said.

Officials familiar with the contents of the book questioned whether there was anything significant in it that could be considered classified.

One official who has followed the issue closely said that it could be difficult for authorities to bring legal action against the book's author because the Obama administration has itself released so much detailed information about the bin Laden raid.

Owen said he had no desire to compromise national security in writing the book. It originally was due to be released on the anniversary of the September 11 attacks, but was moved up a week due to high demand, Dutton said.

"NO EASY DAY is a book that I'm proud to have written. My hope is that it gives my fellow Americans a glimpse into how much of an honor it is to serve our country," Owen said in a statement from Dutton.

"It is written with respect for my fellow service members while adhering to my strict desire not to disclose confidential or sensitive information that would compromise national security in any way," he said.

The author now faces threats against his life. An official al-Qaeda website last week posted a photograph and the real name of the former Navy commando, calling him "the dog who murdered the martyr Sheikh Osama bin Laden."

One of the sources familiar with the official US account of the bin Laden operation said that as US commandos went up the stairs to the third floor of his hideout, the al-Qaeda chief popped his head out of the room where he was hiding, and that commandos shot at him and missed.

This account is not dissimilar, though not identical, to the account now proffered in the new bin Laden book.