PHILADELPHIA – He never knew when the White House summons would come: The president wants to talk, and he has some unscheduled time tonight. Can you get down here?

Later, civil rights historian Taylor Branch, winner of a Pulitzer Prize, would slip into the family quarters of the executive mansion with a pair of microcassette tape recorders and a list of questions, to take President Bill Clinton’s thoughts.

Their discussions, conducted from 1993 to 2001, were so confidential that Clinton squirreled the tapes away in a White House sock drawer. Somehow, they escaped subpoena by the special Whitewater prosecutor (and have yet to be released), but Branch has written a book based on the experience – “The Clinton Tapes: Wrestling History With the President” (Simon & Schuster, $35) – that provides a rare account of a president’s state of mind as events swirl around him.

“It was a pinch-me privilege to do this,” said Branch.

The Clinton encountered here is brilliant, his protean mind ranging from the motivations of world leaders and U.S. political opponents to detailed policy wonkery, theology, history, and sports, in a stream-of-consciousness style. He also is at times moody, self-absorbed and frustrated – but ultimately, in Branch’s telling, a stone idealist.

That facet conflicts with the enduring journo-historical shorthand about Clinton: a tactical political animal who followed polls and had no core beliefs, a soap-opera figure impeached after an affair with a thong-snapping intern. Branch hopes his book will contribute to a fuller understanding.

“He was fighting that myth from the ’60s, fueled by resentments from the right and the left, that government was hopeless except as a scourge and a menace – it could not do anything positive,” Branch said. “He believes we’ve got to find a way to make government helpful, that the essence of patriotism is to find something positive in politics, and if it’s not there, it’s all of our jobs to put it there.”

Among Clinton’s accomplishments, Branch said, were a balanced budget, peace agreements in the Balkans and Ireland, free-trade agreements, the AmeriCorps national service program, and progress on poverty.

Branch dictated as much as he could remember into a tape recorder as he drove home to Baltimore from Washington after the sessions, sometimes parking in his driveway and finishing as dawn was breaking. The talks ran late, beginning well after Branch had already put in 12 hours on his acclaimed three-part biography of the Rev. Dr. Martin Luther King Jr.

Branch and Clinton were old friends, having shared an apartment in Austin while they co-managed the 1972 George McGovern presidential campaign in Texas. They were in some ways alike, two white Southern liberals in a pod, but had drifted apart. Branch became a magazine journalist and Clinton an Arkansas pol.

“We parted ways after the McGovern campaign, partly because of idealism,” Branch said. “I thought he was just on automatic pilot with his political ambition. He wanted to run for Congress. Hillary and I were more alike in that we were discouraged by politics – Nixon was re-elected, Vietnam continued. ... Politics was petty and corrupt. I thought he was a standard politician.”

The two men renewed their friendship after Clinton was elected in 1992, and early in the administration the president said he wanted a candid historical record of deliberations in his White House, proposing that Branch be a sort of court historian on the staff. Branch declined that role, but they settled on oral-history interviews.

Over 79 interviews – about 200 hours in all – Branch was immersed in Clinton. “Each one was a roller coaster,” he said.

There are glimpses into the Clintons’ affectionate marriage, as well as moments when the president interrupts what he is doing to help daughter Chelsea study. And there are tabloid bits:

Clinton said he had “just cracked” when he had gotten involved with Monica Lewinsky, overwhelmed by the death of his mother, the Whitewater investigation, and the Democrats’ loss of Congress in 1994.

“He said he could have done worse,” Branch wrote. “He could have blown something up.”

Clinton thought that George W. Bush had great political instincts but was unqualified to be president, and that John McCain would probably be a good president but had no idea how to win.

The president and Vice President Al Gore “exploded” at each other after the 2000 election. Clinton said he could have garnered enough electoral votes for victory if he had been sent to stump in Arkansas and New Hampshire, two states where he was popular. Bush carried both. Gore said Clinton’s scandals had been a “drag” on him. Clinton said Gore had run a lousy campaign with no vision.

Before publication, Clinton read proofs of Branch’s 707-page book, and the two spent hours on the phone discussing the former president’s concerns.

“To say he was nervous about it would be fair,” Branch said, adding that he did not make any changes in response to Clinton. “He was running hot and cold. It’s pretty personal. ... Most of it is he’s waiting to see how it is received, whether people will focus on just the salacious parts.”

It’s unclear when Clinton will release the tapes. Bound transcripts fill a shelf in his Chappaqua, N.Y., home office.

“I know they will come out sometime,” Branch said. “We wouldn’t have done this if he wasn’t committed to having them available to scholars one day. But he’s been evasive when I’ve asked when he’ll release them. I would guess that it would probably be after Hillary’s career is over.”

Branch, too, wonders how scholars will weigh the tapes.

“I am nervous about it, because one day, whether I’m alive or not, someone is going to judge the quality of the questions I asked, of the information I extracted from him,” Branch said. “I hope I got it right.” The Clinton Tapes: Wrestling History With the President

By Taylor Branch

Simon & Schuster, 720 pages, $35