BAR HARBOR – One of Maine’s most vocal conservation boosters is looking for a new challenge.

Ken Olson, who has led Friends of Acadia for just shy of a decade, intends to leave early next year.

Olson shepherded the group through a doubling of its membership, the creation of a public bus system that removed 558,000 vehicles from a tiny island and the multimillion-dollar birth of the nation’s only endowed trail system.

Now, the president and chief executive officer whose seaside office is piled high with schemes for mass-transit systems, federal budget overhauls and a restoration of Mount Desert Island’s “islandness,” says he has no plans for the future.

“I do want to take the summer off [in 2006] … [But] I can’t imagine not being involved in conservation somehow. … There’s a little left in here – I hope,” said the 58-year-old Olson, touching his chest.

Colleagues have no doubt that Olson’s public service will continue long past this “retirement.”

“Conservation is at the very core of his heart and soul,” Brownie Carson, executive director of the Natural Resources Council of Maine, said Wednesday.

Olson, who lives in Tremont, is mulling several options – including a position with a nationally known environmental group – but isn’t ready to sign anything, he said. Olson sent his letter of resignation to the Friends of Acadia board of directors late last week and plans to move on early in 2006, he said.

In a formal response to Olson’s retirement, board Chairman Dianna Emory of Trenton said she’s sorry to lose his vision but wishes him well.

“What he has given to Acadia National Park … and to each of us, will be there forever,” she wrote. “I hope this means he will take more time to enjoy this place that he loves so deeply and to which he has given so much of himself.”

In the 10 years that Olson has served as president and CEO, Friends of Acadia has grown from 1,500 members and $4.5 million in endowments to 3,000 members and $14 million in endowments. Olson also has played a major role as the 19-year-old group evolved into what Acadia Superintendent Sheridan Steele on Wednesday called “one of the most effective friends groups in the United States.”

Friends of Acadia has always played a more robust advocacy role than many other friends groups, which serve primarily as fund-raisers. “You can’t ask a bunch of Yankees to give up their right to say how government ought to work,” Olson said.

Under Olson’s leadership, Friends of Acadia became a bigger player in Augusta and Washington alike, advocating on clean air and national park budget issues, Carson said.

“I just appreciate the energy and the enthusiasm that he has for Acadia and the state of Maine. … He’s been bringing it to the national spotlight,” said Gov. John Baldacci, who has worked with Olson from the Blaine House and from Washington, D.C., as the 2nd District’s congressman.

Olson’s involvement in larger policy issues, such as his effort to increase the wild nature of the Allagash Wilderness Waterway or to ban personal watercraft throughout MDI, occasionally has made him a controversial figure.

“I have the hide of an alligator,” Olson joked.

But among conservationists, Olson’s enthusiasm for Acadia and his ability to inspire that feeling in others is legendary.

Maine Department of Conservation Commissioner Pat McGowan spoke of Olson’s accomplishment in coordinating volunteers who contribute more than 40,000 hours to the park every year, DOC spokesman Jim Crocker said Wednesday.

“That’s something that we aspire to,” he said. “Ken Olson has built a volunteer organization that has been a national model for parks.”

Wednesday, Olson recalled his first visit to Acadia, as a student from the University of Maine at Orono, when he – like so many other tourists – was struck by the beauty of barren mountaintops rising from a foggy sea.

“My job here has been to remind people of how that simple, visceral emotional reaction to a place really says something about the value,” he said.

“[Acadia] takes your heart,” Olsen said. “You want to care for it.”