RUTH CARSON does not doubt the value of a free press. "It's the newspapers I can't stand," she explains.

When she and her copper-magnate husband were in the divorce courts, extricating themselves from prior marriages, a London paper ran an interview with the first Mrs. Carson, a zoologist, under the banner headline: "Heartbreak Parrot Woman in Plea for Earl's Brother."

"Of all the husbands who ran off with somebody's wife that week," says Ruth "Geoffrey qualified because he had a measly title and if the right 300 people went down on the Royal Yacht, he'd be the Duke of Bognor. Has anyone ever bothered to find out whether anybody really cares? The populace and the popular press . What a grubby symbiosis it is. Which came first? The rhinoceros or the rhinoceros bird?"

Those who have reached theather-going age since 1950 or so will be stunned to learn that this grand speech comes from a play -- Tom Stoppard's "Night and Day."

Since Bernard Shaw's death, English-speaking playwrights have given public issues approximately the same loving care that rose gardeners reserve for Japanese Beetles. The trails blazed by Samuel Beckett and Tennessee Williams, the two great names of the postwar theater, may not have led in precisely identical directons, but both have led squarely away from political matters -- matters, that is, of general interest which are subject, arguably, to solution through collective action.

The modern Problem Play did not surface until the late 19th century, courtesy of Henrik Ibsen. "'A Doll's House,'" said Shaw, "will be as flat as ditchwater when 'A Midsummer Night's Dream' will be as fresh as paint; but it will have done more work in the world and that is enough for the highest genius."

When Shaw died, the Problem Play died too. And the preoccupation with political and economic questions that dominated American theater through the Depression faded from our stages in the '40s and '50s. The thrill of being able to attack the most controversial issues without fear of government reprisal seemed to have worn thin. Playwrights moved on to other things.

That is why "Night and Day" and the current drift of Tom Stoppard's work deserve to be followed with a compass and spyglass. Stoppard has written a play about the role of the press, and his plot, as he will readily admit, is secondary -- perhaps even a bit too secondary. (Anyone who cares to see it more fully developed can consult Evelyn Waugh's "Scoop.")

Stoppard's characters are also secondary. They are there to serve an argument in which each of them -- Ruth, the headline-battered wife played by the magnificent Maggie Smith; Milne, the romantic young freelancer played by Peter Evans; and Wagner, the weary older reporter to be played by Paul Hecht, replacing Frank Converse -- has a stake.

Like Shaw, and unlike Brian Clark, the author of "Whose Life Is It, Anyway?",Stoppard has had the dramatic decency to parcel his wisdom out among several characters rather than make one of them an author's mouthpiece who can lash the others with his acid tongue.

To Ruth's tirade against Fleet Street sensationalism, for instance, Milne has this retort: "It's the price you pay for the part that matters . . . junk journalism is the evidence of a society that has got at least one thing right, that there should be nobody with the power to dictate where responsible journalism begins."

Milne comes closer than anyone else to speaking for Stoppard, but when the talk shifts to the influence of unions on the British press, the intellectual ballast of the play shifts, too. A foreign correspondent, says Milne (who once crossed a picket line to help put out a small suburban paper), ought to be above the petty regimentalism of a labor dispute. "I am not a foreign correspondent," is Wagner's dry response. "I am a fireman. I go to fires. Brighton or Kambawe -- they're both out-of-town stories and I cover them the same way. I don't file prose. I file facts."

"In a good play," the 19th-century German playwright Friedrich Hebbel wrote, "everyone is in the right."

It is not by chance that "Night and Day," although built around an issue, contains Stoppard's richest assortment of characters to date. They are the human outcomes of an effort to carve an issue into distinct points of view, and then to find characters to articulate those points of view with feeling. Stoppard wanted someone scornful of the celebrity-hounding London press -- someone who could convey the pain inflicted by a reckless story. Who better than a celebrity victim? A reasonably innocent celebrity who has been dragged through the headlines at a vulnerable moment in her life.

But it is not enough to have a character passionately declaim against -- or for -- the press. We go to (or leave) cocktail parties for that sort of thing. Stoppard needed a way to add emotional depth to his argument, so he gave his heroine a past affair with one reporter and a current infatuation with another. By this time, she was getting to be a bit of a tart, but also a living symbol of the extremes of a free press: its romantic allure on the other.

"Night and Day" is not the first play of Stoppard's to raise a public issue, but it is the first to do much with the issue beyond raising it. As a result, Stoppard will be hearing a word that drama critics have been keeping in mothballs through the last few decades (except for such special occasions as the opening of a new work by Arthur Miller).

The word is "preachy." It is not a pleasant word. But being called preachy -- perhaps occasionally even being preachy -- is, to quote Jacob Milne, "the price you pay for the part that matters." On Broadway

A hasty inspection tour of the New York theater underscores the daring of "Night and Day." The New York season, so far, is not only short on plays about issues, but short on plays, period. Five of the seven shows that have opened in Broadway houses this fall are musicals, and the standout box-office hit of the group is an extravaganza called "Sugar Babies" at the Mark Hellinger Theatre, with, in order of endearance, Bob Williams and his Wonder Dog, 14 dance girls, Ann Miller, half a dozen leering comics, and Mickey Rooney.

"Sugar Babies" main mission is to bring back the heyday of burlesque, to which end creator Ralph G. Allen has supplied samples from his collection of 5,000 burlesque sketches. Every generation has trouble appreciating its own farceurs, so some will approach this latest piece of multi-million-dollar nostalgia hoping to unearth a lost vein of sparkling American humor in the abandoned mines of innocent sexism. But if Allen's samples are representative, they suggest that burlesque was very, very crude ore indeed.

In one of the show's more sophisticated exchanges, Rooney complains to a breezy hotel clerk that "I've got a leak in my tub."

"You've got to leak in your tub?" says the clerk. "Well go ahead. You paid for the room."

Elsewhere, Miller as a harried school-teacher, asks Rooney, as a precocious pupil, to explain the difference between prose and poetry.

"Oh, that's easy," he answers. "The pros stand on the corner."

With gags like these, one yearns for the physical artistry of a Bert Lahr, not the desperate flailing of Mickey Rooner, who carries the phrase "do anything for a laugh" to new depths of literalness.

Miller, on the other hand is an amazing phenomenon at 55 or 25 or however old she wants to be, cavorting across the stage in top hat and tap shoes and exposing her extremely exposable legs at every opportunity. And when the stars are resting up between turns, "Sugar Babies" offers a terrific tribute to Sally Rand, with dancer Barbara Hanks doing a seductive disappearing act with giant feathered fans, plus a brief appearance by two of the most durable bottom bananas of 20th-century entertainment, Bob Williams and Louis the Wonder Dog.

There have been several wonder dogs since this act made its first appearance 47 years ago, but only one Bob Williams and absolutely no changes in the basic premise: Man instructs dog to do trick. Dog, to all appearances, does nothing. Man rewards dog.

"You see," explained Williams in a dressing-room interview after a performance last week, "I think the dog is great whatever he does."

Williams, a former boxer, and the various Louies, all springer spaniels have performed for presidents (e.g. Roosevelt), queens (e.g. Elizabeth), princesses (e.g. Grace) and fuehrers (e.g. Hitler). qObviously, his act has wide appeal. But he would like one thing clearly understood. The dog could be any dog. "I don't think he has any idea he's performing," said Williams, as Louie lay snoring under the makeup counter. "He doesn't do anything different from what he does at home." m

At the other end of the nostalgia spectrum is an elegantly sung and staged revival of Frank Loesser's "The Most Happy Fella," based on Sidney Howard's play "They Knew What They Wanted." This largely forgotten hit of the late 50s deals with Depression-era wine-growers in northern California, but Cesar Chavez and his United Farm Workers would probably not choose it for a benefit show. Its hero, for one thing, is the owner of the vineyard, a lovable capitalist known to all his workers as Tony, and played with irresistible sentimentality by opera star Giorgio Tozzi.

A bashful, middle-aged bachelor, Tony visits a San Francisco restaurant and leaves a love letter -- on a napkin -- for a waitress he calls Rosabella. Later, they strike up a correspondence, and when Tony's jealous sister warns him he is too old and ugly to think of marriage he sends Rosabella a snapshot of his handsome foreman, representing it as his own.

The musical that Loesser fashioned from this premise was full of warm melodies and primitive lyrics (and only one widely familiar hit song, "Standing on the Corner"). But the relationships among the characters were unusually dark and subtle for a musical comedy, and the show could not ask for a better production than it has here, from its stars to its spectacularly evocative scenery (by Douglas W. Schmidt) to its blissfully unamplified sound.

The list of current New York shows also includes "The 1940s Radio Hour" (which began at Arena Stage last year and is now at New York's St. James Theater), "Peter Pan" (which has moved from the Kennedy Center to the Lunt/Fontanne) and a stage version of "Snow White and the Seven Dwarfs" (now at Radio City Music Hall and headed for the National). Coming are revivals of "Oklahoma" (now on post-Kennedy-Center, pre-Broadway tour), "West Side Story" (which opens at the Kennedy Center in early January), "The Music Man," "Bye Bye Birdie," and "My Fair Lady."

The nostalgia boom, in short, goes right on booming and its impact may soon be felt in the political arena, too. When the Democrats, gather at Madison Square Garden next summer to nominate a presidential candidate, a 20th-anniversary revival of "Camelot," with a 20-years-older edition of Richard Burton, will just have opened. There is a question of fairness here. If the Kennedy forces are to have the strains of "Camelot" wafting like ideological Muzak through midtown Manhattan, surely the Carter team is entitled to some countervailing piece of Southern-fried nostalgia, like a revival of "Tobacco Road."