The fans who approached Lewis Black in a Seattle eatery one recent morning were very polite. Black reacted in kind, genially signing autographs and posing for photos.

The fans knew Black as the impolite comic, witty author and professional grouch who makes funny by railing at the stupidities of Republicans, Democrats, foodies, weathermen, the Old Testament — whatever ticks him off.

It's a long list, fueling many cranky riffs on TV's "The Daily Show" and other programs and a stand-up career so successful he lives half the time on a tour bus.

But what admirers may be surprised to learn is that Black is also a dedicated (if unsung) playwright. ACT is now mounting "One Slight Hitch," his romantic comedy (yes, romantic), that's been 30 years in the making.

Attired casually in jeans and gray sweater, Black offstage is a calmer, nicer but no-less-perturbed version of his raving comic persona. ("My act? It's not an act!")

A self-professed socialist, he declared he's "fed up" with both major political parties.

He decried the effect of Seattle's spring pollen count on his sinuses. "The concept of health out here is shaded in a bogus package," Black groused. "In New York I inhale poison, and I have no allergies."

And playwriting? "You don't choose this! It's a compulsion."

Black, now 63, discovered theater as a 12-year-old in suburban Maryland, thanks to parents who took him to Washington, D.C., to see shows."I liked the extraordinary fact of a room being transformed by a play or a musical. It was more interesting than High Holy Days services and achieved some of the same ends."

As a student at University of North Carolina, he wrote his first play — which he describes as "nauseating, the kind of thing that if I ran for office would come back to haunt me."

But Black forged on ("in theater you learn by failure"), studying playwriting at Yale Drama grad school where his classmates included Marianne Owen, the veteran Seattle actor who plays the rattled mother of the bride in ACT's "One Slight Hitch."

After years as a starving dramatist, with "just enough success to keep me suckered," Black began doing impromptu spiels, inspired by current events, at a New York theater cabaret he ran with friends.

Earning laughs and favorable comparisons to comedy greats George Carlin and Lenny Bruce, Black slid into a profession that's rewarded him with a loyal fan base and a very good living.

But once a playwright, always one. Since the early '80s, he's been writing and reworking "One Slight Hitch," in workshops at theaters in Los Angeles, Washington, D.C., and Tampa, Fla.

Finally, last year, the Williamstown Theatre in Massachusetts became the first company to do a full production, directed by Joe Grifasi (who is also staging it at ACT).

"The problem with the script was that it's a farce and a romance and I had to meld the two," explained Black, who has been in Seattle refining the play for the ACT run.

Reviewing the Williamstown production, The Boston Globe praised "One Slight Hitch" as a "nimble-witted" comedy with "heart," noting that "Black's affection for his characters is palpable throughout, even as he embroils them in the machinations of farce." (The play will also be seen at New Jersey's Georgetown Playhouse next season, co-starring Black's Yale buddy Mark Linn Baker.)

Are more plays forthcoming? Black isn't sure. "I have kind of a love-hate relationship with writing plays. I've written three books, and the question is whether to do a book or a play. The play would be about theater."

Misha Berson: mberson@seattletimes.com