EUGENE — Adapting Ken Kesey's massive novel "Sometimes a Great Notion" to the stage sounds as crazy as trying to cut down an old-growth fir with a pocketknife.

EUGENE — Adapting Ken Kesey's massive novel "Sometimes a Great Notion" to the stage sounds as crazy as trying to cut down an old-growth fir with a pocketknife.

Kesey's 1964 masterpiece, perhaps the quintessential Northwest novel, runs 280,000 words longer than "Moby Dick," and a bit shorter than "War and Peace." It meanders like a swollen river, shifting point of view not only from chapter to chapter but page by page, paragraph by paragraph — even, at times, within the same sentence.

How do you manage all that in 21/2; hours of theater?

Aaron Posner found a way.

"Even though the novel is famously sprawling and wide, and people would call it unfocused, the core story actually has unity of time and place and a very direct central action," Posner said by phone from his office in Red Bank, N.J., where he is artistic director of Two River Theater Company. "Adapting it to the stage was less difficult than people might think."

Posner's adaptation, done with permission of the Kesey family, opened April 1 in Portland and will run through May 10. The play drew a rave review from The Oregonian's Marty Hughley, who called it "an artistic triumph."

Posner, 44, is a Eugene native who delivered newspapers for The Register-Guard as a boy and who graduated from South Eugene High School in 1982.

Though he's lived in the East for two decades, Posner remains an Oregonian through and through. His older brother, Oren Posner, is the founder of Lane Forest Products in Eugene. The Posner family would go to the coast on weekends, traveling through the landscape that inspired Kesey's fictional town of Wakonda, Ore., the setting for "Sometimes a Great Notion."

And Posner is no stranger to adapting big works to the stage. In the past he's done stage adaptations of Fyodor Dostoevsky's "The Brothers Karamazov" as well as works by Kurt Vonnegut.

His adaptation of Chaim Potok's "The Chosen" won the 1998 Barrymore Award for Best New Play.

"Sometimes a Great Notion" took decades to ripen in Posner's mind as a candidate for the stage. He has read the book more times, he jokes, than anyone else in the universe with the possible exception of a handful of Kesey scholars.

"I have read the whole thing through 10 to 15 times," he said. "Not counting pieces here and there."

It is not, he admits, an easy go. Many people bail out before finishing, perplexed by Kesey's studied complexity, which has been compared to that of William Faulkner.

"I honestly can't remember, since it's been 20 years, when it occurred to me it could be on the stage," Posner said. "It twisted its way all the way into my imagination. I loved it. It's so Oregonian. It's this spectacularly brilliant novel, on the scale of my early loves, Tolstoy and Dostoevsky. And it's set in my home state."

Posner visited Kesey himself at the author's Pleasant Hill farm and spent a day talking about the proposed adaptation. Kesey, a theatrical personality if ever there was one, loved the idea.

But distracted by other obligations as well as a sense that he wasn't quite ready for the job, Posner waited until just more than three years ago to begin writing.

Kesey himself had died in 2001, so the playwright contacted Faye Kesey, the author's widow, and obtained a formal agreement for the project. Then he sat himself down for a week in a yurt in Yachats and began to write.

Posner used a lot of dialogue straight from the novel. "At least 50 to 60 percent of the actual lines are Kesey's. It is Kesey's world, and it is Kesey's genius. My craft was to translate that and reshape it into a theatrical event, with the rules of the theater and the shape of the theater."

That first draft was in three acts, like a traditional well-made play; but it served only as a springboard for revisions to come as Posner took his script through the usual process of development.

It was performed in a staged reading in Philadelphia and then workshopped in Portland, becoming a two-act play in the process.

Posner, who directed the production in Portland, continued to tinker right up to the last moment, adjusting the timing on intermission after the show's first preview.

The opening in Portland was attended by Faye Kesey, some of the couple's children, and former Merry Prankster Ken Babbs.