A. R. Gurney likes to write letters. He doesn't like to write speeches.

In a way, that's how his hit play, "Love Letters," evolved.

About three years ago Mr. Gurney was learning to use his home computer. "I was writing letters to my friends as a way of practicing," he recalled in a phone conversation from his New York apartment. "Then I started writing these fictional letters."

Before long the fictional letters began to center around two characters who had been floating around in the back of his mind -- a man and woman who meet as children and carry on a lifelong friendship, tinged with romance. Like most of the characters Mr. Gurney creates -- for that matter, like Mr. Gurney himself -- the pair are upper-middle-class, white Anglo-Saxon Protestants.

Not knowing whether he'd written a play, a short story or $H something else entirely, he decided to experiment with it as a speech. "I had to give this speech at the New York Public Library, and I don't like giving speeches much anyway, so I thought I'll try this out," he explained.

Together with an actress friend, he read the imaginary correspondence. They planned to read just part of it, but the audience wouldn't let them stop.

And "Love Letters" hasn't stopped since.

The distinctive two-person play, which begins a one-month engagement at the Mechanic Theatre on Tuesday, has been "seenby more people and made more money than anything else I've ever written," says the author of three novels and 15 plays, including "The Dining Room," "Scenes from American Life" and "The Cocktail Hour" (which on Friday began a five-weekend run at Theatre Hopkins).

"Love Letters" has been mounted in foreign countries from Japan to Brazil, as well as most of Europe. Even more impressive is the number of actors -- more than 200 -- who have portrayed its archetypal WASP protagonists, Andrew Makepeace Ladd III and Melissa Gardner. The list includes Steve Allen, Diahann Carroll, Kitty Carlisle Hart, Charlton Heston, Timothy Hutton, Diana Rigg, Kathleen Turner and, of course, Colleen Dewhurst and George Hearn, who will be performing it here.

"Love Letters" director John Tillinger, a veteran of five other Gurney scripts, believes audiences respond to these works, and to this play in particular, because the playwright hits a universal chord: "He's very true to feelings, and though the feelings are expressed in a very WASP way, which is often avoidance in one form or another, the feelings are correct."

For actors, part of the appeal of "Love Letters" is that the playwright insists the script be read -- not memorized. "Since the theme of the piece is people who communicate through their letters, it's important that they be locked to the page. It adds a restriction that contributes to the theme," Mr. Gurney explained.

That restriction also means the play doesn't require extensive rehearsals. "What you do is get together one day and go through it," Mr. Tillinger said. In Los Angeles, where "Love Letters" just celebrated its first anniversary, actors regularly step into the roles for short runs between TV or film shoots.

It's also entirely appropriate that the touring production of "Love Letters" coincides here with a production of "The Cocktail Hour," Gurney's semi-autobiographical play about a writer who writes a playabout his family, much to his parents' dismay. "Love Letters" made its New York debut in 1989 at the Promenade Theater. "The Cocktail Hour" was already playing there. However, the producers decided to give the epistolary drama a try on dark nights.

Multiple openings appear to be the norm for the prolific Mr. Gurney. A week from tonight his latest play, "The Old Boy," about the old-boy network in American politics, opens at Playwrights Horizons in New York. Four days later, San Diego's Old Globe Theatre will mount the second production of "The Snow Ball," Mr. Gurney's theatrical adaptation of his 1984 novel of the same name. The story of several prominent Buffalo, N.Y., citizens who restage a popular society ball of their youth, "The Snow Ball" premiered at Connecticut's Hartford Stage in February.

Nor is that all Mr. Gurney is up to. He's also working on a new play, which he'd rather not discuss. And he's "deep into" the screenplay of "Love Letters" for Columbia Pictures. What form this movie will take is difficult to imagine, since much of the "Love Letters" phenomenon rests on the fact that not only is the script read, but the actors sit side by side at a table, not moving or even facing each other.

The screenplay "will be very different," Mr. Gurney acknowledged, explaining that the movie will include secondary characters and "will be much more visually focused. The theme of letter writing will still be there, through voiceovers and things like that, but I'm trying to make it a new thing." And despite the hundreds of actors experienced in these roles, so far the cast has not been chosen.

A screenplay, a script in progress and two new play openings -- an impressive spate of activity for a man who spent a quarter of a century as a humanities professor at the Massachusetts Institute of Technology, from which he has been on leave since the mid-1980s. The 60-year-old playwright was into his fourth decade by the time he had his first appreciable theatrical success --"Scenes from American Life."

In many ways, that play set the tone for his future work. Not only did it dissect the lifestyle of the American WASP -- from coming-out party to country club -- it also provoked the ire of Mr. Gurney's father, a Buffalo insurance and real estate executive. The senior Mr. Gurney was so displeased that he refused to speak to his son. His reaction is reflected to a lesser degree by the fictitious father in "The Cocktail Hour." "He felt somehow that I had violated some trust," the playwright said simply.

As this example suggests, Mr. Gurney follows the adage: Write what you know. His 1977 novel, "Entertaining Strangers," is about a humanities professor at a major, unnamed "Institute of Technology" in the Boston area. After its publication, he was sued by a woman who believed she was the model for one of the characters. The suit was dropped when Mr. Gurney agreed to make some minor changes in the paperback edition.

"The Snow Ball," the new play based on his most recent novel, not only takes place in Mr. Gurney's hometown of Buffalo, but the main character, like his father, is an insurance and real estate executive in a family business.

Although the plot and characters of this lyrical, nostalgic tale haven't provoked any controversy, the Old Globe's production has. Last November, in a move that stirred publicity in theatrical circles, Mr. Gurney resigned from the Dramatists Guild, of which he was secretary. He had chosen to honor his contract with the Old Globe in opposition to the Guild's boycott of resident theaters that refused to accept a standard minimum contract. He denies signing a substandard contract, but, he said, "The Old Globe couldn't guarantee all contracts would be like mine, so the feeling was I had broken ranks."

In other words, a certain degree of hostility is nothing new to Mr. Gurney, whose plays, ironically, feature a life of gentility and politesse. Of all of those plays, the one that hits closest to home is "The Cocktail Hour.""It's about a playwright who's written a play, and the play that you're seeing on stage is in some ways the play that he's written, so it's got a self-reflexive tone to it, so there has to be an autobiographical element to it," he acknowledged.

How did his parents react? For starters, Mr. Gurney didn't write ++ "The Cocktail Hour" until after his father's death. "[Some psychiatrist] might want to argue that I couldn't," he suggested. In addition, he has refused to allow it to be produced at Buffalo's regional theater, the Studio Arena Theatre. Although his mother saw the play in New York and liked it, he feels staging it in her hometown "might make her self-conscious."

While his plays are conservative thematically -- focusing on families and relationships -- they are surprisingly adventuresome structurally, as the unconventional formats of "Love Letters" and "The Cocktail Hour" suggest. "He may have a theme which has been done a hundred different times, but he does find an experimental way of presenting that theme," Mr. Tillinger explained.

In the case of "The Cocktail Hour," Suzanne Pratt, director of the Theatre Hopkins production, said, "While I'm familiar with some plays-within-plays, this is the only example I know of an author's describing the play that you're watching while you're watching it." As a director, she said she relied on the text as an "immediate tour guide. I've taken it quite literally."

At one point in "The Cocktail Hour," the father says, "The life we led is completely gone." The playwright agrees. Furthermore, he said, "I don't necessarily think it's a bad thing."

Granted, many of his plays deal with the disappearance of that life-style. But considering his predilection for toying with theatrical form, you might think he'd be tempted to toy with subject matter as well. And he is tempted, Mr. Gurney admitted.

But, he added, "I always say that, then I find myself having one more thing to say."

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'Love Letters'

Where: Morris A. Mechanic Theatre.

When: Tuesdays to Saturdays at 8 p.m.; matinees Wednesdays and Saturdays at 2 p.m., Sundays at 3 p.m. Through May 26.

Tickets: $17-$32.

Call: 625-1400.

'The Cocktail Hour'

Where: Theatre Hopkins, Merrick Barn.

When: Fridays and Saturdays at 8:30 p.m.; matinees Sundays at 2:15 p.m. Through May 26.

Tickets: $7 and $8.

Call: 338-7159.