Harp and Soul : Trends: By happy accident or serendipity, Irish music is becoming hip. The Fenians and their devoted following prove it at a Costa Mesa pub.

It doesn’t seem like much of a formula for success: form a band, get a regular gig before a mostly young crowd and then spend at least half the evening playing songs that are hundreds of years old and tell of bloody war, lost love, bitter conflict, revolution, poverty and mystical legend.

Yet the Fenians have been making it work for three years at the Harp Inn in Costa Mesa, packing the place on Friday and Saturday nights (and with a slightly truncated band on Thursdays) with patrons who not only listen, but often dance and sing along. It’s all a matter of being in the right place at the right time with the right music, they say.

The Fenians may be the best-known Irish band in Orange County, making their home in the county’s best-known Irish bar, in a time when Irish music--from the lyrical ballads of O’Carolan as played by the Chieftains to the edgy modernity of the Pogues--is becoming, of all things, hip.

Not that the Fenians necessarily need a hook. The people who come to hear them at the Harp Inn, and occasionally at other clubs and festivals in the Orange County area, know what they’re going to get. They are either thoroughly devoted fans of Irish music or have become, usually in short order, thoroughly devoted converts. Particularly on Friday and Saturday nights, the Harp is packed full, with a line out the front door. The talk inside tends to be expansive and loud, competing with the volume of the music, and no one who knows the words is shy about singing along.

The crowd may originally have come for the rock ‘n’ roll set that follows the Irish music set on Fridays and Saturdays--the band plays both styles--but many of them show up early anyway. Ambivalence appears to be nonexistent.

None of this surprises the quartet. They came to Irish music in much the same way, by happy accident or serendipity.

For instance, band leader Terry Casey, 29, is from an Irish-born family and is the only family member born in the United States. He grew up hearing Irish music (his father played the tin whistle and flute), but he turned to playing rock ‘n’ roll guitar as a teen.

He gave up the instrument a few years ago, however, and began working as a general building contractor. It wasn’t until he attended a party at a friend’s house that the musical spark was reignited.

“My friend’s dad and my dad were best friends,” said Casey, “and all those old Irish parties seem to turn into sing-songs. They started singing an old immigration song called ‘Spancil Hill’ and at that moment--I think it was in 1987--I said, ‘So that’s what it is.’ I was sick of playing Top 40. I decided, gosh, that was what I wanted to do.”

Casey found himself playing “the only five Irish songs I knew” at an Irish bar in Laguna Niguel. He came back the following Friday and was asked to play regularly.

“I realized then I had to learn about 40 songs. I raided my mom’s Clancy Brothers collection and tried to get every Irish record I could get my hands on.”

Later, he translated his guitar talents to a mandolin he bought for $50.

Like many Irish bands, the Fenians are a product of evolution. A handful of players have come and gone since Casey began shopping for musicians in early 1989. Brendan Harkins, 25, the band’s current bass player, joined two years ago. He tells of wandering into the Harp Inn one night and striking up a conversation with Casey about Irish music. Soon after, the band’s bass player left and Casey offered Harkins a spot.

“Our family is Irish from a few generations back,” said Harkins, “and every St. Patrick’s Day we used to go to a parade. When I was about 9 or 10 I played in a kazoo band in the parade. We did ‘McNamara’s Band.’ That was my first exposure to Irish music. Other than that, it was my mom and dad walking around the house singing ‘Molly Malone.’ I think it was the only Irish song they knew.”

Guitarist Rob Williams, 39, heard his first bit of true Irish music at an Irish restaurant in Los Angeles in the early 1970s.

“I was just there for dinner, and I heard the Irish Beggarmen do ‘Black Velvet Band,’ and I was hooked immediately. I’d liked all forms of ethnic music, but I’d never been exposed to Irish music.”

He continued to play rock ‘n’ roll until 1979, when he joined an Irish group performing aboard the Queen Mary. That band evolved into another group that was eventually called the Bold Fenian Men and appeared at the Harp Inn. It has since disbanded.

Andy Mendoza is the Fenians’ newest member in the Irish set (the band recently added Ian Jones, a saxophonist, for the rock set). Mendoza, 23, first saw the band play about a year ago.

“I used to come and watch them play on a few weekends,” he said. “It looked pretty fun, like they were having a good time up there. When they asked me to sit in, I rose to the occasion.”

Together, the four create an atmosphere both intimate and boisterous, not unlike that of a singing pub in Dublin, such as O’Donaghue’s, where everyone sings and no one moves because no one can.

Williams described the popularity of Irish music as being infectious. “I don’t think there are more venues around for Irish music,” Williams said, “but I do see more involvement, people coming to places where Irish music is being played. . . . You get hooked. A lot of people . . . come up to us on the break and say, ‘I’m here for the first time and this is great music. I love this music.’ ”

Williams also sees a resurgence, saying years ago he “saw the Chieftains at the auditorium at Anaheim High and it was half empty. Last year they sold out the Performing Arts Center.”

And many tell the band members that their dad “used to play that when I was a kid and my mother sang those songs,” Casey said.

But he insisted that the band and its music are not locked in the past.

“Out style is definitely modern,” he said. “We’re modern guys. In Southern California, when you’re 16 and you get a guitar, you don’t say, ‘I want to sing “Danny Boy,” ’ you want to play rock ‘n’ roll and be a rock star. So we bring that energy, the tempo changes and all that, and infuse it into our music. We play some very old songs, though, like ‘Star of the County Down.’ Some of the melodies are 700 or 800 years old, and they’re steeped in tradition. But it’s folk music; it’s music of the people, and it can change every generation, every decade.”