It's Saturday night at the Irish Festival in Baltimore, and the headliner needs no introduction. To a chant of "We want O'Malley!" a man in black clambers onstage and strums his six-string, striking a pose like some sort of Gaelic guitar hero.

With no further fanfare, the band rolls into an Irish folk-rock song, "The Body of an American." Leading the charge from center stage is Martin O'Malley, Baltimore's Democratic mayoral candidate and, for this night, the undisputed life of the party.

With a Guinness within easy reach, O'Malley leads a couple of thousand Irish-Americans in a passionate sing-along, soaring through the chorus: "I'm a free-born man of the U.S.A."

For 90 minutes, he will jump and dance. He will stop to raise another pint. He will sweat and sing some more.

"If he proves to be as good a mayor as he is an entertainer, we're in for a treat," says Michael Keeney, a community organizer from Southwest Baltimore wearing an O'Malley campaign T-shirt.

State Del. Ann Marie Doory, a Baltimore Democrat, adds: "It's really cool when your new mayor plays Van Morrison."

O'Malley, who won the Sept. 14 primary election after a bitter campaign, faces Republican mayoral nominee David F. Tufaro in the November general election.

On Saturday night, O'Malley's March closed the slate of entertainers at the city's three-day 25th annual Irish Festival, which ended yesterday.

Todd Stephens, a lawyer from Pasadena, says O'Malley's win is cause for a celebration of ethnic pride. With his hands wrapped around an Irish coffee, Stephens says, "The Irish aren't on top all the time. Why not flap your wings?"

During the day, some of the musical acts inserted O'Malley's name as the hero in their traditional ballads. Told of this, O'Malley says, "The highest of all Irish honors -- to have a ballad in your name."

O'Malley, 36, lawyer and city councilman, got his first taste of Irish music while growing up in Bethesda. But it was the maudlin stuff of acts such as the Clancy Brothers. In high school, he discovered Irish rebel music, the kind with bite. He learned to play the tin whistle and listended to the stories of poverty, persecution and fierce determination that are the foundations of Irish nationalism.

A few years later, he traded the whistle for a guitar, and a Celtic rock band was born. He called it O'Malley's March and the group became a regular at Irish pubs from Baltimore to Ocean City.

The group didn't play much the past few months, its leader absorbed with running for the city's highest office. But you could count on seeing the band at the Irish Festival. It hasn't missed the event in years.

At the festival, O'Malley concentrates on the music and makes scant mention of "that mayor thing."

Early on, he brings up the fact that he's wearing a long-sleeved jersey, and not the black muscle shirt that is his trademark stage gear.

"I want to apologize for the sleeves," he tells his audience.

Earlier, in a quieter moment, he explains the change in wardrobe: "I haven't been able to get to the gym in three months."

But if he's flabby from time missed from the weight room, he may soon flex more power than he ever imagined.

During the show, politics are mentioned, but mostly in the scheme of British oppressors and the bad hand dealt to the Irish. The one reference to Baltimore politics and his mayoral campaign is an attempt to incite the crowd into a little more singing and clapping and dancing.

"I've been to a lot of Baptist churches lately, and let me tell you, they beat the heck out of you Catholics when it comes to participating," O'Malley tells the audience.

By the time O'Malley's March ends its set with a medley built around a reel titled "The Salley Gardens," more people are dancing.

In the middle of the medley, O'Malley interpolates a song from the Irish rock band U2 and sings words that seem to speak of his campaign and the final step he must take before he can implement his vision for Baltimore.

He sings: "I have run, I have crawled, I have scaled these city walls, only to be with you. But I still haven't found what I'm looking for."

Through the night, one question hangs: If he wins the November general election, can a Mayor O'Malley find time for music?

O'Malley refers the question to his wife. "Katie wants me to give it up. She's just afraid I won't know my children till eight years down the road."

Katie O'Malley says she's unsure whether her husband should continue to pursue his avocation.

"We're looking for a balance," she says. "If it all falls out of balance, unfortunately, no. But if it stays within the balance, sure -- every now and then."