MILWAUKEE — John Mellencamp has long had a split personality. He's half bar-band attitude, a blues-rock heir to the Rolling Stones tradition who once called himself "Little Bastard." His other half is the socially conscious folk-rocker who wrestles with race and class issues and helped initiate Farm Aid.

Those two personalities fed off one another Friday night at the Marcus Amphitheatre, when Mellencamp alternated top-40 hits such as "Jack and Diane" and "R.O.C.K. in the U.S.A." with such weightier fare as "Paper in Fire" and "Cuttin' Heads," a new song that comments pointedly on racial politics in hip-hop. Distorted garage-band guitars held it all together.

Mellencamp opened with a cover of the Stones' 1969 classic "Gimme Shelter." By kicking off the show with one of Jagger and Richards' most brutally paranoid tracks, the artist formerly known as John Cougar set the tone for a show that took fans down memory lane with little nostalgia.

He followed "Gimme Shelter" with the new R&B-tinged "Peaceful World." While the recorded version features singer India.Arie, longtime backing vocalist Pat Peterson ably picked up the slack here during Mellencamp's call for racial unity.

Only then did Mellencamp and his nine-piece band give the audience a dose of old-school Cougar, delivering a supercharged, Bo Diddley-style take on his 1982 hit "Jack and Diane." After running down "Key West Intermezzo," a lively "Minutes to Memories" and a playful "I'm Not Running Anymore," Mellencamp returned to more serious material with "Cuttin' Heads."

The title track from his upcoming album, "Cuttin' Heads" is an aggressive rocker about an interracial couple in Mississippi fighting old stereotypes. During the song's middle section, however, percussionist/vocalist Moe-Z M.D. laid down a stinging rap (written and delivered on record by Chuck D) about rappers using the "N" word and creating new stereotypes involving gold jewelry and bling-bling.

The first of three of the night's more intense tunes was followed by "Paper and Fire" and "Crumblin' Down," both of which came across harder in person than on record. Mellencamp barely cracked a smile through this trilogy, screwing his eyes shut with an almost pained intensity that conveyed the message that rock and roll is serious business.

He lightened and loosened up for the solo acoustic "Woman Seem," a bitingly funny look at male/female relations. Then he stripped off his button-down shirt, rolled up his T-shirt sleeves and let it rip with a set-closing stretch that included the laughing-to-keep-from-crying "Full Catastrophe of Life," "Authority Song" (featuring a snippet of AC/DC's "Back in Black") and the anthemic "Pink Houses."

After this rousing finale, the single-song encore of the midtempo "Your Life Is Now" felt anticlimactic. Yet the tune's seize-the-day sentiment logically concluded an evening as much about the message as the music.