Steve Coll, The Washington Post's managing editor for six years, said yesterday he is stepping down at year's end to pursue book projects.

Coll, 45, who will continue with The Post as a part-time editor and writer, reached the decision after finishing his book on terrorism, "Ghost Wars."

"This is the work I feel like I'm supposed to be doing, what I do best, where my passion lies," Coll said from New Orleans, where he was finishing a family trip. "In the end I felt this is who I am and who I felt I wanted to be since I was 17."

He added: "I was not unhappy in my job," but that "there are certain aspects of management no sane person would enjoy."

Executive Editor Leonard Downie Jr. said he was initially "shocked" and tried to talk Coll into changing his mind. But, he said, "I knew he missed writing in many ways. I saw the fun he had doing that book and what satisfaction it gave him to do that. . . . He's been a marvelous leader in the newsroom, a perfect partner for me."

Downie said he will pick a new No. 2 editor by November and is considering several high-ranking Post editors. Newsroom sources, who declined to be named while discussing personnel matters, said three assistant managing editors had already been asked to submit memos outlining their views of the job: Eugene Robinson of Style, Liz Spayd of the national desk and Philip Bennett of the foreign desk.

Asked to assess his tenure, Coll said: "I helped a lot of reporters reaffirm the paper's commitment to investigative and innovative reporting of all kinds." He said Downie, a former managing editor who succeeded Ben Bradlee in 1991, had been "generous" in granting him a wide berth. But at times, Coll said, "you feel pretty far removed from journalism" as a manager. "That was somewhat frustrating for me."

The announcement stunned the staff, just as Coll had been a surprise choice in 1998, when he won the job over several older and more experienced editors. A former Post correspondent in New York, New Delhi and London who had written four books, Coll was editor and publisher of The Post's Sunday magazine at the time.

Several editors and reporters credited Coll with invigorating the paper, particularly on longer investigations and projects. He pushed hard for the front page to include more pop culture subjects, such as television and music. But some staffers said the sheer size of the paper cushioned his impact and that Coll, who spends little time circulating in the newsroom, remained a remote figure for many reporters.

Senior editors were full of praise yesterday. "He wasn't afraid of long stories or spending time to do things as well as they could be done," Robinson said. "He was a favorite of writers and very easy and fun to work with. It helped that he's well known as a writer and journalist. That gave him a lot of credibility in the newsroom."

Said Spayd: "Steve is one of the most brilliant people I've ever met, and his presence will be greatly missed. He imposed a lot of new ambitions on the paper in the past six years that I hope we can carry on once he moves to his new love."

Downie called Coll "an inspiration to a lot of our most talented editors and writers" and said he had made a mark on matters as diverse as narrative journalism, personnel decisions and the paper's Web site.

At Downie's urging, Coll talked to Post Co. Chairman Donald Graham and Publisher Bo Jones before making a final decision. Downie said he sees Coll's future role as comparable to those of Bob Woodward and David Maraniss, two best-selling authors who remain involved with The Post.

A Montgomery County native, Coll shared the 1990 Pulitzer Prize in explanatory journalism with Post colleague David Vise for a series on the Securities and Exchange Commission. He said his next book, for which he has not yet signed a contract, will also be about national security. "Ghost Wars," an investigative look at the CIA's role in Afghanistan, reached No. 8 on the New York Times bestseller list.

Coll, who would have been the leading contender for the top job once Downie, 62, steps down, said he was aware that his boss has no plans to vacate the post anytime soon, a position Downie confirmed yesterday. The Post has no mandatory retirement age.

Coll also said family considerations -- the younger two of his three children are still in high school -- were a factor in his timing. As a senior editor, he said, "you can't control your time. Every time a fire bell rings, you go down the damn pole."

Steve Coll's decision surprised the Post newsroom. At year's end, he will become a part-time editor and writer.