Jesse L. Martin is an actor given to character analysis and criticism. Consider his observation: "The only people who make transitions, wallow in them, are actors. [Other] human beings never do."

Martin, who recently joined NBC's "Law & Order" as volatile detective Edward Green, explained: "Because `Law & Order' is so story-driven, emotional changes occur quickly, just the way they do in life. For an actor who has been trained to agonize over every shift in feeling, that's a challenge."

Between shooting scenes on Manhattan's Upper West Side -- with no shortage of female onlookers -- Martin talked about his alter-ego, a bit of a loose cannon with a reputation for unorthodox strategies. Often at odds with his partner, Lennie Briscoe, played by Jerry Orbach, and his boss, Anita Van Buren, played by S. Epatha Merkerson, Green arrived with more than one complaint leveled against him for using excessive force.

"He is passionate about his work, but more than that, he is passionate about life and knows how to live life to its fullest," said Martin of his character.

In his trailer, parked several blocks from where the cast was rehearsing on a fall day, Martin defended Green.

"Eddie is unpredictable," he said. "He may leave work, go to Atlantic City and gamble all night, but he'll be back on the job in the morning. He's able to move from his outside life to his career seamlessly. He can lose his temper. And he can be lovable. He's like everyone else, only he's a New York City cop."

Before this season, Martin, born 30 years ago in Rocky Mount, Va., was best known for his recurring stint on Fox's "Ally McBeal" as Dr. Greg Butters, Ally's love interest. Martin also played a disenfranchised alien on "The X-Files."

He co-starred in the hit musical "Rent" as Tom Collins, the gay computer analyst who falls in love with Angel, the doomed drag queen. He also was a member of the John Houseman Acting Company, where he honed his Shakespearean skills.

But he said that landing a principle role on "Law & Order," NBC's Wednesday night series now in its 10th year, was a career high point. Like many actors in New York, Martin wanted a guest spot on the program, and he auditioned several times to do just that, he recalled.

"At one point I was offered a guest spot, but I turned it down because it was a very small part and I felt it was worth waiting in order to get a better one," he said. "It wasn't really a gamble. I knew if I took the smaller role, the odds were I wouldn't be called back for a bigger part."

Martin never landed that guest spot. Instead, he replaced Benjamin Bratt, the latest departee in the series' customary turnover of lead players.

Eddie Green is very different from Bratt's character, Martin noted: "I am a more aggressive detective than he was. And my relationship with my partner, Briscoe, is wary, unlike the more relaxed relationship he had with Bratt.

"The biggest challenges in playing Eddie is dealing with the harrowing stories. One of the most disturbing was `Killers' [about one child killing another]. I know it's all make-believe, but there was something about seeing that child -- I know he's an actor -- lying there dead in a tube, with his pants pulled down around his ankles. If that doesn't disturb you, nothing will."

In the same episode, Green used some morally gray tactics in questioning a suspect. Holding her hand and evoking an avuncular figure, he practically seduced a confession from her.

"My interaction with that child was uncomfortable, but perfectly justified," Martin said. "It needed to be done. With perpetrators, you have to assume they're criminally minded and deal with them accordingly. You have to use every human skill -- not just police skill -- to achieve your goal."

Martin was interested in analyzing Green only from the performer's viewpoint. Questions about how viewers see Green were of little interest to him.

"I never thought about it," he said. "And since there is no way of my knowing what audiences feel, I don't concern myself with it. Their responses would have nothing to do with my performance or how I approach the role. I suppose there might be some differences between how audiences see Eddie, but that has more to do with the reactions of individuals, rather than demographic groups."

As Martin tells it, earning the role of Eddie Green was a combination of pleading and keeping his options open.

"When I heard that Benjamin Bratt was leaving the show, I went to [executive producer] Dick Wolf and basically begged for it," Martin said. "He said, `When I come to New York in a few weeks, we'll get together for an audition. If you get any other offers, let me know.' "

In the interim, Martin was offered two television development deals. "I didn't know what a development deal was, and when I found out -- it's essentially sitting around L.A. waiting for either someone else or myself to come up with a TV story that I would star in -- it was not especially attractive," he said. "I had no idea what I wanted to do, except I didn't want to be in L.A." After all, his friends, family and his cat Marley -- named for singer Bob Marley -- all live in or prefer the East.

Nevertheless, when Wolf heard about Martin's two offers, said Martin, "he offered me the role of Edward Green. And I didn't have to audition for it. I was handed a brief bio of who he was and that was it. I've used that description as my bible, although I've had some input, too."

Brought up in Buffalo, N.Y., the son of a truck driver, Martin earned his degree in theater from New York University by working as a bartender and waiter. At the John Houseman Acting Company, a non-profit, off-Broadway operation, he was a "utility actor."

"That means that when other actors had to leave for whatever reason, I'd take over. These were mostly small roles. We toured the country doing Shakespeare, and I appeared in `Romeo and Juliet' and `Two Gentlemen of Verona,' among other plays. So far I have not been typecast because of race."

He hopes eventually to play the roles of Othello, Hamlet, Malvolio "and anything by August Wilson."

The turning point in his career was co-starring in "Rent," a stint about which he had some reservations initially. "It's not that I didn't like it -- I just didn't get it, specifically its connection to `La Boheme' [on which `Rent' is loosely based]. When you're auditioning, you only see bits and pieces of the play. So I didn't really get a sense of the whole thing."

When he was offered the plum role in "Rent," Martin took it mostly because he needed money for his own rent. As it turned out, "Rent" became a theater event, garnering every top theater award including the Tony Award and Pulitzer Prize. He was with the show for 2 years, including six months in London.

"Rent" also was a major steppingstone that led to his role on "Ally McBeal."

"Michelle Pfeiffer and [executive producer and writer] David Kelley were in the audience at `Rent' one night," he said. "I am told -- and it's really just a rumor -- that when David was looking for an actor to play Dr. Greg Butters, he was looking at tapes of various actors, including mine. And Michelle said, `I remember him from `Rent.' Hire him.' "

Recently Martin has added producing -- co-producing, to be precise -- to his rsum with "Fully Committed," a critically and commercially successful off-Broadway show about the experiences of a waiter in an upscale restaurant.

At the moment, however, his thoughts are focused on "Law & Order" in general and Eddie Green in particular.

"I'd like to learn more about Eddie's personal life and find how that informs his work -- his decision to be a detective and the way he deals with his job on a day-to-day basis," he said. "I do know that Eddie has an estranged relationship with his father, a petro-chemical engineer who wanted Eddie to follow in his footsteps. We will find out more about that relationship. Will Dad ever show up? No idea. Will Eddie have a romance? No idea."

He flashed his smile.

A knock at the door indicated that shooting was about to resume. Martin subtly morphed into Eddie Green, his posture and expression shifting just slightly as he left the trailer.