Richard Greenberg, a nice, sensitive, rotund sort who wouldn't swat a fly — and couldn't swat a fly, even if you lobbed the ball up to him at 10 mph — has been unkind to a woman named Janet Kain. How? Well, at the age of 38 or so, he discovered baseball. Discovered it? He plunged into it.

"Janet Kain is my sister-in-law, my brother Edward's wife. I've known her since I was 11," says playwright Greenberg. "The males in my family" — a Long Island family — "are fanatical baseball fans, and have been all their lives. I was the one guy who was interested in other things, and the only one Janet could talk to in baseball season. So when I came over and joined the club, she was the only person in the family who was not happy."

It was during the 1998 World Series, when the New York Yankees were sweeping the San Diego Padres in four straight, that Greenberg joined the club. "One day I happened to turn on the television, and it was the World Series, and it was" — he searches for the exact word — "riveting. I couldn't understand what it was I didn't like about baseball, hadn't liked about it."

That was then, this is now. Greenberg's always precise and fresh-peeled use of words, spliced to what for him is a whole new language — the living, breathing vernacular of baseball, heightened here and again by Greenberg with words one might not normally expect from baseball players (synthesize, extrapolate, congeries, paradigm, austere) — is one of the lovely strengths of Take Me Out, the baseball drama that after batting .407 in (yes!) London, England, and then Off-Broadway's Joseph Papp Public Theater, has now reached the big leagues, the playoffs, at the Walter Kerr on West 48th Street.

"Whoever wants to know the heart and mind of America," critic and teacher Jacques Barzun wrote nearly 50 years ago, "had better learn baseball, the rules and realities of the game." Whether Mason Marzac has ever read Barzun is not known, any more than we may know if Jacques Barzun could ever have imagined a great baseball player (let's say New York Empires all-star center fielder Darren Lemming) who's also an out-of-the-closet homosexual, but here, in Take Me Out, is Mason Marzac — a discreetly gay, sensitive resident of New York's Chelsea district — talking to us about what has brought him, Mason, "with no little excitement," to realize that "the perfect metaphor for hope in a Democratic society" is baseball:

First, it's the remarkable symmetry of everything. All these threes and multiples ofthrees [three strikes, nine innings, nine players, etc.], calling attention to . . . the game's noble equality . . . Everyone is given exactly the same chance . . .

There's none of that scurry [of other sports] . . . In baseball there's no clock . . . Another thing I like is the home-run trot . . .

This discourse of Mason's is also, the man who created Mason admits, "a history of how I fell in love with the game, though I think he [Mason] needs it more than I did. He'd felt an absence of something, which is what gave it such surprising force. In my case there was not such a void."

Greenberg addresses the parallel as he nurses a cup of tea in Moonstruck, a West 23rd Street diner — his "office," the late Helen Merrill, his agent, called it — not far from his own Chelsea residence. How did the author of such thoughtful plays as Three Days of Rain, The Extra Man and Hurrah at Last so perfectly acquire Take Me Out's baseball lingo? "By reading and by listening. That vocabulary is what I loved most — it was so immediately attractive — and I was immediately immersed. Like a crash course at Berlitz."

If some of the ballplayers in Take Me Out are astonishingly intelligent and articulate (though some are stupid as sin and, in one instance, baseball in hand, murderous), Greenberg is not astonished. Look at David Cone, he says — "because I love that word he invented when he spoke of the year in which so many Yankees lost their fathers as 'kind of tough to eloquate.'" Or Derek Jeter, who on "Saturday Night Live," "where so many trained actors have come to grief, was so at ease, and so skillful, and so funny."

Greenberg says he's a Mets fan except when the Mets are playing the Yankees. "My favorite part of the past few seasons was when the Mets were 24 games out of first place with 24 games to play — and almost made it." The thing is, all of Richard's brothers and cousins were and are rabid Yankee fans, so, by osmosis . . .

The playwright has never met any actual professional ballplayers — "Isn't that odd?" — except, one day at rehearsals, former Mets first baseman Keith Hernandez. Greenberg would be delighted if any big-leaguers came to the show, though he doesn't suppose gayness "is an active topic" on the diamond. Did many members of what's clumsily dubbed the gay community come to Take Me Out when it was at the Public? "I don't know. I think so. We had gratifyingly mixed audiences, but I think they came out in pretty good force."

The thing is, Take Me Out is not a play about gayness, though it's that, too. It is also about life, death, mortality, bigotry, hero worship, hokum and, above all, in Greenberg's words — he was speaking of Derek Jeter — "the perfect balance between individuality and the submergence of that individuality in teamliness." Let's go to the replay: Take Me Out is a play about the heart and mind of America, and a beautiful one.