YOU can think of nine-time Grammy winner Bonnie Raitt’s music career like a circle.

She got her first guitar at 9 — “It was a $25 Stella I got for Christmas from my grandparents and my folks, together, from Sears.” Today, Raitt, 59, runs a guitar program for kids around the country. “We’re particularly targeting girls,” she says. “It helps their self-esteem.”

She dropped out of Rad-cliffe College but wound up being awarded the Harvard Arts Medal, alongside Harvard dropout Pete Seeger. The medal made her happy, she says, “because the last time I was in that administration building, we took it over during the Cambodia invasion [in 1970] and I was in a band called the Revolutionary Music Collective and we played for the strikers out in Harvard Yard.”

And she’s been friends with bluesman Taj Mahal for almost 40 years — “I opened for him at Skidmore College in 1971,” Raitt recalls. Now the two are touring together, with equal billing, in a show playfully dubbed “BonTaj Roulet,” which touches down here tomorrow night in Prospect Park, one of the benefit shows to support the Celebrate Brooklyn! series.

Part of the proceeds from ticket sales on the tour go to one of four causes: blues and music education, social justice, environmental protection and safe and sustainable energy. “That’s wind and solar and no nukes,” says Raitt, a longtime anti-nuclear-power activist who doesn’t buy the current thinking about clean nukes. (Check bontaj.com for details about the charities.)

Despite her long history and high profile with a number of causes, Raitt says she’s a musician first, activist second. “People come to see me because of my voice, not because of my activism,” she says.

When she was younger, Raitt hadn’t even been planning a career in music. “Most people really have a dream of being a star, work at their music so hard. I worked at my music, but as a hobby,” she says.

Raitt, who had an uncle who worked for the social-action Quaker group American Friends Service Committee, majored in social relations and African studies. “My plan was to go over to Tanzania and do that kind of work,” she says.

The daughter of Broadway singer John Raitt and pianist Marjorie Haydock, California-born Raitt comes with a certain musical pedigree. But her own music runs more to mixed breed — rock, R & B, folk and blues, with Raitt’s signature bottleneck so flexible, she wouldn’t be out of place in the Allman Brothers.

Raitt came into folk music early on. “I was trying to change the world, sing those protest songs, playing in school assemblies,” she says. “Bob Dylan and Joan Baez and Pete Seeger were my heroes.

“But on the other side, at the after-school dances . . . the Isley Brothers’ ‘Twist and Shout’ probably spontaneously put me into puberty right there.” She adds Fats Domino and Chuck Berry to the musicians she went “absolutely nuts” for, along with The Beatles and the Rolling Stones, Ray Charles and Motown. And old-time bluesmen like Mississippi Fred McDowell, for whom she opened at some New York Clubs at the start of her career.

Redhaired Raitt (her white streak, she says, “is definitely the only natural color I’ve still got”) is clearly still enjoying her rockin’ self. “I’ll be 60 this year. Can you believe this? I mean, none of us thought 60 was gonna be feeling like 30,” she says.