When Doris Kearns Goodwin was still young and unknown and writing her biography of former President Lyndon B. Johnson, she stayed at his Texas ranch. Sometimes, she said later, when he could not sleep, he would settle into her bed and confess his troubles while she sat nearby.

Walter Isaacson was at Steve Jobs' bedside as Jobs was dying of cancer, an experience, Isaacson has acknowledged, that made him "deeply emotionally wrapped up" with his subject.

Contemporary biography has always been a tricky balancing act, even before Paula Broadwell demonstrated with her book about David Petraeus how the scales can tip decisively the wrong way.

The challenge of writing a biography about a person who is still alive is that an author must first establish trust and a comfort level with a subject to get access and a free flow of information. But the biographer is still expected to evaluate and expose unsparingly.

There's no road map to follow because publishing houses acquire all types of biographies -- from serious historical tomes to quick turnarounds about of-the-moment public figures -- and do not have clear boundaries for authors on how to achieve their objectives.

"Any biography of a living, breathing and active figure who's still at the height of his powers is going to have to strike a delicate balance between access and objectivity," said Tim Duggan, executive editor at HarperCollins. "It can be very tricky, and it requires real finesse."

Even in the wake of revelations that Broadwell was having an affair with Petraeus, then the director of the Central Intelligence Agency and the subject of her biography, "All In: The Education of General David Petraeus," editors and biographers alike were loath to condemn the book outright because the rules in this area are so hazy.

"I suppose it ultimately depends on the book," said Stephen Rubin, president of Henry Holt, "though I would prefer if they didn't have sex, because you lose a sense of perspective objectivity when you are romantically linked."

Goodwin, now a critically acclaimed biographer of historical figures like Abraham Lincoln and Franklin D. and Eleanor Roosevelt, has always asserted that her relationship with Johnson was not sexual, and that she sat in a chair while he unburdened himself from her bed. Still, most reviewers have agreed that the portrait she paints of Johnson, the 36th president, was far more empathetic than the one that emerged from his most famous biographer, Robert Caro.

Similarly, the highly respected Isaacson showed Jobs' most unsavory flaws but often portrayed them as character traits that enabled him to achieve tremendous things at Apple.

Scott Moyers, who acquired Broadwell's book for Penguin Press, has turned down many requests for an interview on the subject. But Vernon Loeb, an editor at the Washington Post who was Broadwell's co-author for "All In," wrote in an article published Tuesday that it was clear that Penguin was paying for the unusual access -- and that neither he nor Moyers was inclined to press too closely on why Broadwell had it.

The editors wanted "a book on the rigors of command told from an inside point of view," Loeb wrote in the Washington Post, adding, "I had no say over the book's ultimate take on Petraeus, which some have found excessively laudatory."

Though the book is not officially an "authorized" biography, in practice it has all the hallmarks of one, including extensive interview time with Petraeus in Afghanistan, often on the six-mile runs he would take with Broadwell.

The question that publishers are grappling with now is whether they have a responsibility to scrutinize more closely the reasons behind the special access. Publishers who saw the manuscript when it was being shopped around said that there were plenty of red flags.

For one, they said, Petraeus was at the height of his military career and had as much to lose as gain by participating in such a biography. Even more unlikely is that he would have cooperated on someone else's book instead of hiring a ghostwriter to produce his own, controlling the writing process and burnishing his own image. Also odd, they said, was that he worked with someone who was not an experienced writer -- to the point that a co-author, Loeb, had to be brought in to do the heavy lifting.

Authors who have written biographies of living people say it is highly unusual for subjects to display this kind of trust to outside writers, and they are not so sure they would want it. Generous access has its pitfalls, including the risk to a writer's credibility.

"There are great perks -- you are seeing your subject in real time," said Douglas G. Brinkley, a history professor at Rice University who has written biographies of Sen. John Kerry, former President Jimmy Carter and Rosa Parks. "But the downside is you can't do hagiography, and if you do, you will get called out hard."

Carol Felsenthal has written biographies of Katharine Graham of the Washington Post, Si Newhouse of Conde Nast and former President Bill Clinton, and none of them cooperated.

"There are not a lot of journalists who would want to be involved in an authorized biography," she said. "If you get too close to your subject, you are nothing more than a transcriber, and readers should know that."