Jason Alexander always imagined he'd be a stage actor. For years, he worked steadily on Broadway ("Merrily We Roll Along," "Broadway Bound," "Jerome Robbins Broadway" -- winning the Tony Award for best actor in a musical). Then a chap named Larry David helped lure him to Los Angeles to co-star in David's quirky sitcom "Seinfeld," and that changed everything.

Now David has enticed Alexander back East, to replace him as the star in his Broadway comedy "Fish in the Dark," running at the Cort Theatre through Aug. 1. Alexander plays Norman Drexel, a frazzled, self-absorbed guy (sound familiar?) bedeviled by a dying father, greedy relatives and the revelation of a scandalous family secret.

Alexander, 55, who earned seven Emmy nominations as the frazzled, self-absorbed George Costanza on "Seinfeld," lives in Los Angeles with his wife Daena; they have two sons. He spoke with Newsday contributor Joseph V. Amodio backstage in his dressing room.

Must be nice to be back in your old stamping grounds. You were a Jersey boy who moved to the city?

Yes. And my wife's a Long Island girl. From Plainview. We'd visit her parents there like every weekend, especially in summer.

Back when you were a struggling actor?

Right. Believe it or not, I had a motorcycle back then and used to tool it out on the LIE with my wife on the back.

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How'd your in-laws react?

They didn't care. It was my mother. [Morphing into Mom's voice.] "You're gonna kill her! And you're gonna kill yourself!" [He laughs.]

Is your take on "Fish in the Dark" different from Larry David's?

Often, replacements are just asked to duplicate the actor who played the role before. But there were things Larry did that . . . didn't feel right for me. Larry said, "I'm not an actor, I don't know what I'm doing. Change it -- do your thing." Which is great. The script is bulletproof. Really funny. It's stupid funny when Larry does it because he comes from what I call the "Oh, shiny" school of acting.

Oh . . . shiny?

Say you're in a moment with Larry -- he'll write it to a fever pitch, this intense conflict, then someone enters who has nothing to do with this and Larry just turns and it's like he goes, "Oh . . . shiny."

Like a baby distracted by shiny objects.

He'll just drop your moment -- done -- and move on to the next one. Whole new emotion. We did that on "Seinfeld," but there'd be a scene break, a cutaway. But onstage . . .

It's a little jarring to switch moods on a dime?

I'm looking for more connective tissue . . . the arc of the character. Larry will tell you, he eighty-sixed many things in the development of this play because he said, "I can't play anything too serious . . . too feely."

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Did you advise him when he was writing the script?

Noooo. After he decided to perform in it, we had lunch -- he asked, "What am I in for?" and I tried to tell him what to expect. Like how in the third week of rehearsals, when everything's going great, all of a sudden it falls apart, and you think, "It's no good, I'm no good." But it comes back together. He said, "Why does it fall apart the third week?" and I said, "Nobody knows. But it does. Always. So don't panic." I also tried to explain the lifestyle and commitment of eight shows a week. You're not going to play golf in the afternoon and do a show that night. Or have two or three drinks after -- or go to a loud restaurant and try to talk over the noise -- you won't have a voice the next day. You have to be monastic about life when you're on Broadway.

Larry's script, this character -- it must feel familiar.

Absolutely. We grew up experiencing a lot of the same things. Our families are crazy New York Jews. We grew up hearing those New York Jewish rhythms. That's what he writes. Like Neil Simon. There's a music to that writing I thoroughly understand.

Is that why New Yorkers loved "Seinfeld" so?

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There's something about "Seinfeld" that just impacts the city a little differently than anywhere else.

So . . . are you being monastic?

Well, my wife and I found a little place in East Hampton -- I get two days off in a row each week. It'll be nice to get out of the city for a bit.

Will you pull out the ol' motorcycle?

Ohhh, no, those days are gone. Once we had kids . . . my wife made me sign a document that basically read, "I will never again ride on a motorized, two-wheeled vehicle." [He chuckles.] I told her, "Y'know, this isn't legal or anything." She just looked at me and said: "SIGN IT!"

You signed?

Ohhh, yeah.