Even if they didn’t have their programs, many theatergoers at the Maine Center for the Arts will quickly recognize the lead actress in “They’re Playing Our Song.” The musical, which will be staged at 7 p.m. Thursday, March 29, features James Walsh as songwriter Vernon Gersch and, as his lyricist partner Sonia Walsk, Erin Moran.

For 11 years, Moran came into American homes as prototypical younger sister Joanie Cunningham on “Happy Days.” She exited that series for one year to star with Scott Baio in the short-lived spinoff “Joanie Loves Chachi,” featuring Joanie and Chachi as the lead singers in a rock band. Both returned to the parent series for its final season, getting married in the last episode.

Of the cast, veteran character actors Marion Ross and Tom Bosley have gone on to star in subsequent series. Ron Howard became a superstar director-producer. Anson Williams and Henry Winkler went behind the cameras, Williams becoming a busy director and Winkler a successful producer.

Joanie Cunningham, known for her all-purpose rebuttal “Sit on it!”, was the role that made Erin Moran. But being so closely associated with Joanie has also stifled Moran’s acting career in the 16 years since “Happy Days” ended. Since then, she’s had occasional guest spots on such gathering places for former TV stars as “The Love Boat,” “Hotel,” “Murder, She Wrote” and “Diagnosis: Murder.”

“It is still an impediment to my career,” Moran said by phone. “Thank God for theater. The more popular you were, the more they want you.”

“They’re Playing Our Song,” with book by Neil Simon and music by Marvin Hamlisch and Carole Bayer Sager, is the story of the tumultuous relationship, both professional and personal, of Vernon and Sonia.

Moran joined the cast of the touring production in late January. (Previous stars on the tour had been Barry Williams of “The Brady Bunch” and Cindy Williams of “Laverne and Shirley.”)

She described her character, Sonia, as “very intelligent and too nice to a fault. She collaborates and falls in love with a composer. But her old boyfriend causes turmoil and causes them to fall in and out of love.”

What does Moran like best about the musical?

“The songs and singing them,” she said. “They’re such great songs, and it’s so much fun to act and sing with them.”

Even though she grew up in front of the camera, Moran is a relative latecomer to theater. Her prior experience was recently playing Bella in Simon’s “Lost in Yonkers.” She said it wasn’t much of a transition moving onto the stage.

“‘Happy Days’ was shot in front of a live audience, so it was the same, except for the cameras,” she explained.

Moran has been acting for 34 of her 39 years. She signed with a children’s talent agency at age 5, and soon began acting in more than 40 TV commercials for brands including Crest, Kellogg’s Corn Flakes and Three Musketeers. At age 6, she made her feature film debut in “How Sweet It Is,” starring James Garner and Debbie Reynolds.

She followed that up with starring roles in the TV series “Daktari”(1968-69) and “The Don Rickles Show” (1968). Her other feature-film roles as a child actor were “Happy Endings,” “Watermelon Man” and “Eighty Steps to Jonah.”

Then came “Happy Days,” the story, set in mid-’50s Milwaukee, of Richie Cunningham, his family and his friends. The star was meant to be Howard, fresh off his turn in the 1973 hit film “American Graffiti,” but the breakout star was Henry Winkler as the Fonz, the greasy-haired, leather-jacketed motorcycle kid who made the girls swoon.

At age 12, Moran was already a veteran of three-camera shows when she started the role of Joanie on “Happy Days.” But she learned in other ways.

“There was getting in touch with emotions and letting them out, getting in touch with all the colors of the character,” she said. “Also there was getting together and forming such a bond, such a friendship, within the cast that they became a second family.”

More than a decade after it left the air, “Happy Days” is still going strong in cable reruns, most recently on Nickelodeon. What’s the secret to its enduring appeal?

“It was a good family unit, the morals are there, as are the positive story lines,” Moran said.

Moran’s run with “They’re Playing Our Song” lasts until April 11. Then what?

“I would love to do a feature,” she said. “I wouldn’t mind doing Broadway. That would be a trip and a half.”

Even though the role of Joanie has been a mixed blessing, Moran doesn’t mind getting recognized for it.

“I still get recognized to this day,” she said. “I enjoy seeing that smile on someone’s face when they recognize me, enjoy making them happy.”

For tickets to “They’re Playing Our Song,” visit the Maine Center for the Arts box office or call 581-1755.