THEATER : Hospital Tales : They both got their acting start in New York at different times, and now Len Lesser and Alan Feinstein find themselves in ‘Cold Storage’ at the Gnu in North Hollywood.

Len Lesser has been in “Cold Storage” for a long, long time.

“For 10 years, I’ve wanted to do this play,” says the actor, who has a recurring role on NBC’s “Seinfeld” as Jerry’s annoying Uncle Leo. “Most of my life, I’ve been very shy. When people would say, ‘I don’t want to do it,’ I’d put it away. But this I stayed with.”

After years of working on scenes from the play in acting class and trying to get a production mounted, Lesser’s wish has come true: On Thursday, he opens at the Gnu Theatre in Ronald Ribman’s work, a relationship story of two patients who meet in a hospital ward.

“Although serious things are discussed, it’s very, very funny,” says co-star Alan Feinstein, who originally hooked up with Lesser and the play in acting class. Feinstein describes his character, Richard Landau, as “a family man, an investment adviser in fine art who’s in the hospital for exploratory surgery. So his condition is open. Parmigan (Lesser’s character) is the older man, more ill, and exploring his mortality. He seeks to make contact with the younger man in an emotional and intellectual manner.”

“It’s not heavy, sad, traumatic,” emphasizes Lesser, a veteran of hundreds of TV shows and plays--most often playing the villain--who co-starred in last year’s stage hit “Cantorial” at Actors Alley. “It’s quite funny, moving, profound, rich, textured in language and understanding.”

Lesser’s palpable enthusiasm for the work (originally performed off-Broadway in 1977) extends to his character, whom he describes as “kind of a meshugenah : an outrageous Armenian, intelligent, wonderful . . . all the things I am.”

Although he’s obviously close to the material after so many years, Lesser praises director Jeff Seymour for challenging him to look at the work anew. “I know the play, I know the lines; it would be very easy to be glib,” he admits. “But I was hoping for an adjustment. And the whole time in rehearsal, Jeff kept backing me down--to being real, in the moment, being myself. Every little section we went over: ‘Let’s try this, let’s try that’--experimenting, finding the real person.”

Lesser, who was born in New York, made his debut there at 16, playing Lenny in “Of Mice and Men” at the theater group Juvenile House.

“There was such a sense of exhilaration and power,” he recalls, “communication I couldn’t get in real life, and love coming over the footlights.” After graduating from New York City College at 19 (he studied economics and government with an eye toward going into foreign service), Lesser did a stint in the Army during World War II. Returning to New York, he began working with the American Theatre Wing and appeared in summer stock and on live television. In 1954, he moved to Los Angeles.

Feinstein, too, is a native New Yorker. He began acting in his early 20s, studying at the Dramatic Workshop. After 10 years in two soap operas--”Love of Life” and “Edge of Night”--he was cast by Tennessee Williams as Stanley in the 1973 25th-anniversary Broadway production of “A Streetcar Named Desire.”

In 1975, he headed for Los Angeles, where his credits include the TV series “The Runaways,” the miniseries “Masada,” and the role of Diane Keaton’s callous professor and seducer in the 1977 film “Looking for Mr. Goodbar.”

Last year, Feinstein did his share of heavy stage roles, segueing from back-to-back productions of “The Tempest” to “Macbeth” to “Long Day’s Journey Into Night.” The part in “Cold Storage,” he notes, is equally demanding of his energies--”in a different way. There is a third character, a nurse, but it’s a small role; basically, it’s just these two guys. So it’s a lot of work. A piece like this builds quietly: It’s very focused, takes a lot of concentration. I think it will catch people by surprise.”

Where and When What: “Cold Storage.” Where: Gnu Theatre, 10426 Magnolia Blvd., North Hollywood. When: 8 p.m. Thursdays through Sundays. Closes March 7. Price: $15 to $20. Call: (818) 508-5344.