“We were dealing with acceptance and adaptation, and both had to do with the fact that we were not part of the moneyed elite,” Mr. Kakugawa said.

Mr. Kakugawa, who spent seven years in and out of prison for drug offenses beginning in 1996, said he pressured Mr. Obama into drinking beer.

But Mr. Obama did not smoke marijuana during the two years they spent time together even though it was readily available, he said, adding that he never knew Mr. Obama to have done cocaine. “As far as pot, booze or coke being a prevalent part of his life, I doubt it,” Mr. Kakugawa said. He had graduated, however, by the time Mr. Obama was in his junior and senior years, when he wrote that he most frequently used marijuana and cocaine “when you could afford it.”

Mr. Obama describes a scene during that period where, in the meat freezer of a deli, he watched someone named Micky  “my potential initiator”  pull out “the needle and the tubing,” apparently to shoot up heroin. Alarmed, Mr. Obama wrote that he imagined how an air bubble could kill him. Neither Mr. Kakugawa or the others interviewed for this article who knew Mr. Obama at Punahou recalled hearing that story from him.

During his freshman year at Occidental, Mr. Obama and his dormitory mates would congregate around a couch in the hallway of their floor while stereos blasted songs by bands like The Rolling Stones, Led Zeppelin, The B-52’s and The Flying Lizards. The conversations at Haines Hall revolved around such topics as the Soviet Union’s invasion of Afghanistan that year, President Carter’s proposed revival of draft registration and the energy crisis.

Mr. Obama displayed a deft but unobtrusive manner of debating.

“When he talked, it was an E. F. Hutton moment: people listened,” said John Boyer, who lived across the hall from Mr. Obama. “He would point out the negatives of a policy and its consequences and illuminate the complexities of an issue the way others could not.” He added, “He has a great sense of humor and could defuse an argument.” Mr. Obama seemed interested in thinkers like Friedrich Nietzsche, Sigmund Freud and Jean-Paul Sartre, whom he studied in a political thought class during his sophomore year. The professor, Roger Boesche, remembers Mr. Obama as very serious and not shy about disagreeing.

Mr. Boesche also has memories of him at a popular eatery on campus. “He was always sitting there with students who were some of the most articulate and those concerned with issues like violence in Central America and having businesses divest from South Africa,” he said. “These were the kids most concerned with issues of social justice and who took classes and books seriously.”