Rehab Was Sobering Experience for Her : Pop music: Marshall Chapman, who opens for Jimmy Buffett tonight in Irvine, says treatment put her on the road to self-discovery and balance.

Jumping on the back of a Harley, racing at 100 m.p.h. in the dark with the headlights out--while she was drunk. This used to be how country-roots-rocker Marshall Chapman got her thrills.

But in recent years, the South Carolina native has a different outlook on life and a new definition of excitement. Thanks primarily to an intensive, 4 1/2-week rehabilitation program for substance and alcohol abuse in 1988, Chapman discovered the sense of balance that eluded her for so long.

“My stay at that treatment center . . . was the turning point in my life,” Chapman, 46, said during a recent phone interview. “Drugs, alcohol, promiscuity--it all caught up to me in a big way. I had to re-evaluate everything.”

Currently on tour as Jimmy Buffett’s opening act--with a stopover tonight and Saturday at Irvine Meadows--Chapman and her quartet, the Love Slaves, are sober and having a blast.

“The whole tour [which began on the East Coast in April] has been such a surprise . . . and so much fun,” the talkative, lanky musician said. “I’ve learned how to take care of myself. I mean, I used to lose 25 pounds in three weeks on the road.

“Now, everyone in the band drinks Evian, takes vitamins and munches on fruit. It sounds corny, but we have to take care of ourselves because we want to keep playing. This is what I know I want to do for as long as I can do it”.

After graduating in 1971 from Tennessee’s Vanderbilt University, where she also was a basketball star (she’s 6 foot 1), Chapman worked for a while waitressing at the nearby Red Dog Saloon.

Independent, smart and sassy, she soon was honing her musical skills and was signed by Epic Records in 1976. Her debut, “Me, I’m Feelin’ Free,” earned modest sales but was critically praised (she was hailed by some as “a female Mick Jagger”).

She was cut loose by Epic after two more recordings when her professional and personal life fell into turmoil. But bad times can create fodder for good writing, and her tales of heartache and self-doubt have been recorded by a variety of artists, ranging from Emmylou Harris and John Hiatt to Dion and Joe Cocker.

Influenced by Elvis, Big Joe Turner, Hank Williams and Bob Seger, Chapman embraced country, roots, rock and rockabilly without prejudice. Over time, her own sound and style emerged while creating bouncy, up-tempo shuffles and slower-paced, introspective ballads.

A recurring theme in her rich body of work has been the liberation and empowerment of women. The key, suggests Chapman, is self-esteem.

“I grew up in the South with a family [that had known] wealth for many generations,” she said. “But women had no intrinsic value. Our worth was tied to who we married. This attitude perpetuates a low self-image. For years, I only felt good about myself if I had the right guy.”

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Chapman has transformed many of her mistakes into first-rate songs filled with emotion and detail. From alcoholic-boyfriend blues (“Booze in Your Blood”) to surviving a bad relationship (“Bad Debt”) to heart-wrenching loneliness and withdrawal (“Girl in a Bubble”), she weaves a thread of personal responsibility, dignity and perseverance.

For Chapman, these traits recently found an unusual but receptive audience for the recording of her latest album, “It’s About Time. . . .”

Recorded live at the Tennessee State Prison for Women and released this year on Buffett’s Margaritaville Records, the spirited, 15-song collection developed cautiously. Chapman said she waited three years before accepting the warden’s invitation to perform there.

She confessed that the warden’s warning that “we have no idea how you’ll be received” had her trembling. Eventually, though, Chapman set her fears aside and stepped up to the plate. And judging from the enthusiasm building throughout the recording, she won over a crowd that initially was little more than curious.

“I picked songs that I felt these women could relate to, like ‘Bad Debt’ and ‘Late Date With the Blues,’ ” explained Chapman. “In fact, during the encore [‘Good-Bye Little Rock ‘n’ Roller,’ a song about a mother-daughter relationship] I saw two women cryin’ and huggin’ each other. It was very emotional and very gratifying.”

If not for sheer luck, Chapman readily acknowledged, she could easily have wound up behind bars herself. And the realization that invisible prisons can be just as intimidating keeps her focused and inspired.

“The search for love and freedom is an ongoing journey, and that prison door can shut any time,” she emphasized. “Now when I come up against a problem or confrontation, I have the right tools to deal with it. I have finally found that balance in my life. We’ve all grown up so much during this tour . . . and that’s truly been exciting”.

* Jimmy Buffett & the Coral Reefer Band and Marshall Chapman & the Love Slaves perform tonight Irvine Meadows Amphitheatre, 8800 Irvine Center Drive, Irvine. 8 p.m. Also Saturday. Both shows are sold out. (714) 740-2000.