When Gordon Bowie conducts the Bangor Band, he thinks about his predecessors, Albert Sprague and R.B. Hall, who ushered the band from the 18th to the 19th century. He imagines ladies clutching parasols and gentlemen sporting straw boaters enjoying lively marches and operatic overtures on the green. And he wonders what the 21st century will mean for one of the nation’s oldest community bands.

The past and the future are on Bowie’s mind a lot these days. He will pick up his baton and conduct the Bangor Band for the last time Sunday, Aug. 31, when the band performs at the 10th annual Celebration at Cascade Park. Bowie, who has led the group for the past 12 years and has been a member since 1966, is moving to Washington, D.C., next week.

Bowie rattles off facts about the band’s history as if he were practicing scales on his bass trombone. “It is celebrating its 138th consecutive season this year. … It is the oldest performing arts organization in Bangor, and one of the oldest continuous community bands in the nation. … It’s performed free summer concerts for more than 125 years. … The band has never had an operating deficit.”

Tall and big-boned, Bowie probably could have devoted his life to basketball rather than music. But ever since his childhood days on Long Island, music, especially march music, has been ringing in his head. Bowie wrote his doctoral thesis on Bangor’s most famous bandmaster, R.B. Hall, and has written several marches himself, including “The U.S.S. Maine.”

“I love the band and the band loves me,” he says during a break from packing for the move. “It has been a good and happy collaboration. … My greatest contribution to the band as a conductor is probably that I’ve brought the members a long way musically. I’ve also made the band more forward-looking, putting a big focus on the upcoming turn of the century.”

Bowie is credited with initiating a $100,000 endowment fund to preserve the band’s long tradition, obtaining a recent grant from the Maine Humanities Foundation, organizing the band’s vast music library, and lowering the average age of players and audience members.

“Without gilding the lily any, most conductors have brought us to a higher standard and a new way of looking at the music,” said band President Samuel D. Wyman Jr., 75, who has played tuba with the band for 58 years. “But Gordon [Bowie] has been both a conductor and an administrator. His help with fund raising, grant proposals and other aspects of the band will be sadly missed, along with his skills as a conductor. It’s going to be difficult to fill his shoes. He gave a lot of himself to the band.”

But the Bangor Band is not the only local musical organization Bowie has been associated with. He has played with the Bangor Symphony Orchestra 32 years, one year longer than he’s played with the band.

“He’s made a meaningful contribution to the orchestra in many capacities over the years,” says Robert A. Bahr, BSO general manager. “He’s played principal trombone, bass trombone, served on the board as orchestra liaison, and been very active with our education programs, youth competition and youth concerts.”

Although Bowie is moving to Washington, where his wife, Mary, will work for the Association of American Medical Colleges, he is not retiring. He has accepted an invitation to play with the National Concert Band, and plans to devote more time to his music publishing company, Serendipity Press.

“I have more to do than I can shake a stick at,” he says, laughing. “I’ve been asked to conduct in that area before, and always had to turn it down because of my commitments here. I keep getting asked by musician friends down there, `Come sit in with us’ or `Come play here with us … .’ I’m excitedly looking forward to the changes that are coming.”

As conductor, Bowie has been responsible for selecting all the music the band performed at its 17 concerts each year, helping the musicians learn the programs at weekly, year-round rehearsals and preparing band members in music and spirit to perform. He compared conducting a band or orchestra to coaching a team sport.

“I take talented players and put them on the court,” he says. “They have some skills, but no cohesion, no idea what it takes to play as a team. I have led the band to more refined playing, teaching, I hope, by example and expectation. Together we’ve worked on tempo, flexibility, intonation and precision. … For myself, I have reached musical maturity with them.”

But Bowie leaves with a few things yet undone. While the band produced a cassette recording three years ago, it has not had the opportunity to record a CD. Nor has it been able to expand its program and perform year-round. And while Bowie has attracted “younger — under 45 — musicians,” the majority of the band’s players are over 60, as are audience members.

“My leaving is not the end of things for the Bangor Band,” Bowie says. “The band’s main strength, one of the reasons it has survived and will continue to survive, is that it is an incorporated entity with a constitution and a strong organizational basis. This is a chance for the band to explore its future with a new conductor.

“And I will be back. I’ll be back because of the music. Bangor hasn’t seen the last of me yet.”

The Bangor Band will perform at 5 p.m. Sunday, Aug. 31, at Cascade Park. The program will include two marches composed by Bowie.