Forty-Seventh Street partakes fully of the Times Square ambiance -- traffic congealed into puddings of irritability, food aromas that alone can elevate your cholesterol level, street people with complexions that resemble blue cheese. In this tangy precinct of the theater district there is a cultural event indicative of the changed political climate. Conservatism is no longer "Off Broadway," metaphorically or literally.

Michael Frayn's play "Benefactors" is an autopsy on a particular social sensibility. The title is sardonic; would-be helpers often are not. Although set in London, the theme is transatlantic, and timeless. It begins, in flashbacks, in 1968, the emblematic year of recent radicalism. It ends about a dozen years later, with this message: "It was people. That's what wrecks all our plans -- people."

David, an architect, has plans to develop public housing in a run-down neighborhood. The people he would benefit? "They're going to get their houses pulled down whether they like it or not. And we don't need to ask them what they want instead because we know." And: "I'm not going to build towers. No one wants to live in a tower."

But what begins as an idealistic venture in "building the new world" becomes, in maddeningly minute steps, the torture of a thousand cuts. Politics and bureaucracy and economics and society -- in a word, reality -- compel compromises that drive David toward building high-rise towers. His cynical neighbor warns of "progressive collapse," a technical term for a form of disaster in tall buildings. In Frayn's hands the term has another meaning.

Frayn has not written anything so tiresome as a play "about" -- heaven forfend -- public housing. And it is not "Waiting for Righty," a Thatcher-era emulation of Clifford Odets' "Waiting for Lefty," the paradigm of a play as a political cartoon featuring cardboard heroes and villains. Many political plays, like many political persons, are barren of ambiguity. Frayn's play is about ambiguity, about how personal relations and social actions have, in the end, unanticipated consequences, and how they have, at the beginning, unacknowledged motives.

Frayn has mastered the delicate art of making a point without preaching. "Benefactors" is primarily about the troubled marriages of two couples who become ruinously entangled as they try to "help" each other. However, the private and public situations become mutually reinforcing metaphors. Marriages are, Frayn says, like public works of architecture, plagued by unexpected complexities, changing conditions, defective materials.

Architecture has frequently been invested with political hopes, especially by behavioralists who believe that social nurturing can overcome human nature. They say: reform the social environment and you will reform man. Urban renewal can evict the old Adam.

In the 1930s, a bright light of the literary left, W. H. Auden, wrote in a poem about "new styles of architecture, a change of heart." That thought now looks like a quaint stick of period furniture from a mentality that has all but vanished. (There actually are photographs of the collapse of liberalism -- the 1972 dynamiting of St. Louis' huge Pruitt- Igoe public-housing project. It had become unlivable, a paradigm of giantism and overreaching by liberal social engineering.)

In "Benefactors" the reality principle is incarnate in David's wife, Jane, played with icy force by Glenn Close. Jane is an anthropologist, a student rather than a savior of people: "Look, I'm not trying to help anyone. . . . I'm just trying to count them." For David, the retreat from "building high" is, in several senses, a matter of coming down to earth. When his neighbor says of architecture, "It must be wonderful to change things," he replies: "No, it's not, Sheila. It's heartbreaking. It's always just warped windows and condensation problems. It was going to be so new and amazing, and it never is, it's always just like everything else."

The area he was supposed to benefit is called a "twilight area" -- not a slum, "a bit gray and exhausted, that's all." And so, in the end, it remains, and David, the would-be benefactor, resembles it.

Frayn's conservatism is not Reaganite conservatism with a smiling face, conservatism singularly lacking in a tragic sense of life, gloomy only about government and cheerfully convinced that everywhere else -- a k a, the "private sector" -- is a realm of harmony and limitlessness. Political stances often are products more of sensibilities than philosophies, and Frayn's sensibility is of chastened hopefulness. It is sensibility congenial to an older conservatism.

In the 1960s Frayn was a wonderfully unenthralled columnist in "swinging London" amidst the post-imperial giddiness of Carnaby Street and pop music. Today "Benefactors" is playing next door to "Oh! Calcutta!," a soiled remnant of the 1960s, years when people were told to solve the problems of living by "getting in touch with their feelings." "Benefactors" performs conservatism's thankless task, saying: It's more complicated than that.