D. L. Coburn is willing to comment on the theater's current love affair with human mortality.

"I hate it," he says.Then he remembers that his agent also represents the author of "Cold Storage," a play about a man who has terminal cancer and a second man who fears he does. But the practical politics of the theater cannot derail this tirade once Coburn has gotten up stream.

"Ronald Ribman may want to take a crack at me," he says, But somehow in some perverse way drama is being twisted around. . .

"The drama is life-not life in the face of death, life in the face of life is what drama is about. Therehs absolutely nothing funny about cancer."

Coburn thinks Michael Cristofer, author of "The Shadow Box," is an outstanding playwright. "I don't question their gift," he says. "What I question is why we have this succession of plays about people facing death. . . "We have to get away from this or the terminal patient will be the theater. And I don't consider 'The Gin Game' to be in that bag at all."

Coburn, a 40-year-old former advertising executive who lives in Dallas, wrote "The Gin Game," his first play, in 1975.It has now been running for a year and a half on Broadway, directed by Mike Nichols and starring first Hume Cronyn and Jessica Tandy, then E. G. Marshall and Maureen Stapleton as two gin-rummy players in a cut-rate rest home. The play opens Wednesday night at the Eisenhower Theater, with Cronyn and Tandy in the leads, and will remain here through May 12.

Coburn won't say just what "The Gin Game" is really about, but he is happy to clear up one potential misunderstanding: It is not, essentially, about old people.

"I don't know why my characters got older," he says. "They weren't old when I started." And they aren't about to die, either. "They could live for another 20 years. Christ, I hope they do."

After his characters did mysteriously become old, Coburn began to study the problems of elderly Americans, particularly in nursing homes. "Many of these people are quite difficult to deal with," he says. "They have just about ceased living. . . But on the other hand many people are quite alert and they're distressed to be in such an environment.

"Old people haven't been portrayed as individuals very often," he says."They have been portrayed as old people."

Coburn has special cause to be weary of all the other playwrights dealing in somewhat similar material: People are starting to confuse their plays with his.

When one theater critic included "The Gin Game" on a list of 1977's Ten Best Plays, Coburn was naturally gratified, but the objected to the critic's capsule description of the play.

"I called him up and said, 'My play's not about death and dying; and if that's the way you feel about it, you shouldn't have included it.'" Whereupon (according to Coburn), the critic launched into a discussion of two-character plays and why he had never much liked them: "I'm always waiting for someone to knock on the door," the critic explained. "But yours isn't a two-character play, is it? There's that Puerto Rican nurse."

There is no nurse, Puerto Rican or otherwise, in "The Gin Game." "He was thinking of 'Cold Storage,'" explains Coburn chose to make his two characters older was that Hume Cronyn and Jessica Tandy are older.

"They're remarkable," he says. "There are not too many people like that."

There are certainly not too many theatrical couples who have been married 36 years and who will, in this age of the quick movie and TV buck, stay with a play after its first flush of success in New York.

Coburn says Maureen Stapleton, who replaced Tandy on Broadway, told him: "If I had their money, there's no way I'd go around the country touring. I'd do it for six months and get out."

"The questions comes up, not infrequently, why do we do it?" said Cronyn during a phone interview from Milwaukee last week. "We were both conditioned by a tradition that was created by people like Cornell and Hayes and Lunt and Fontanne who, whenever they had a success, always took it out across the country. That was standard then. Now it's unique.

"Every new city, you have to adapt to a new theater, generally a different audience, always new critics and new judgments. You can't grow fat and sloppy the way one is tempted to do if you're set for a year's run on 44th Street."

From Washington, Cronyn and Tandy will take "The Gin Game" on to London, Moscow and Leningrad. Then they plan to spend a few months at the Stratford Festival in Ontario, where Tandy will appear in "Coriolanus" and "Long Day's Journey Into Night," while Cronyn concentrates on the play he is writing (with collaborator Susan Cooper).

His play is about old people, in Appalachia.