"TELEVISION'S going to have a marvelous effect on theater," remarked Lawrence Langner, co-founder of the Washington Square Players and the Theater Guild, the most prolific producer of his day. That was 30 years ago.

Like most prophets, Langner was both right and wrong.

The Eisenhower's remarkably satisfying "The Dining Room" and New York's Best Musical Tony winner, "Nine," are examples of how TV freed, even inspired, playwrights. The recent Tony telecast itself showed the harm TV can do to the theater.

In "The Dining Room," playwright A.R. Gurney Jr.'s creativity is most evident in the marvelous way he uses the image shorthand that TV has accustomed audiences to grasp. Artifices -- such as slow exits, overheard remarks and confidences -- are avoided, and the pacing is more of today's world, pointed and speedy. With but six players for some 50 roles of all ages, Gurney creates a mood of humor, tenderness and respect for the WASP way of life supposedly passing.

In writing style not unlike the pointillism of Seurat, Gurney creates a mosaic of characters and incidents over the past half-century within many dining rooms. Designer Loren Sherman has delineated just one but it clearly represents many, just as the children, parents, oldsters and interlopers become people we know, once knew or recognize as rugged relicts. Scenes shift, families change, houses alter, time becomes now present, now past -- a melange of common memories.

The challenge to the players, headed by Frances Sternhagen and Barry Nelson, is the need to indicate age, condition and circumstance with instant clarity. The character changes are not effected by elaborate tricks, with make-up switches or any such devices. Director Trainer has had the wit to see that the more simply this intricate play is acted, the more impressive its effect.

With "Nine," the same swift alterations are achieved within the mind of the central figure, a movie director in a professional jam and sexual tangle. Writer Arthur Kopit's script is uncanny for its facility of leaping seamlessly, as minds do, from one unrelated topic to another. He trusts his audience to adjust itself. And it can, because for a couple of generations -- since "The Great Train Robbery" and daily TV made this standard procedure -- we've been able to take in the idea that all sorts of things happen simultaneously. Our minds have been raised to multiple-track action, catching different images on different tracks.

This isn't entirely new. Shakespeare recognized much of it instinctively. His were not, in the classical sense, well-made plays. Gone were the unities of time, place and action. Throughout his plays, comedy fuses with tragedy, much as it does in life itself.

But before a playwright breaks the rules, he must understand them. Not all the newer writers do. Somewhere there must be structure, which too many recent efforts lack. Television may have made it easier for playwrights to abandon the conventions of the past, but too many are ignorant of the whys and wherefores of those conventions.

The gloomier side of Langner's crystal-gazing lies in television's contempt for its audience.

The medium began promisingly enough. Has anyone ever considered that one reason "The Golden Age of Television" came to be was that only the relatively elite owned sets? This early audience was perceived to have enough curiosity to latch onto the new and enough sense to recognize what was alive and vital.

But instead of being a most marvelous educator for mankind, TV quickly turned into a shill.

We come to this year's Tony night, the theater's worst capitulation yet to TV.

Where were the stage figures? The bill was laden with TV names. Surely the lowest point was Cher's turn as Mary Martin singing Cole Porter's "My Heart Belongs to Daddy." What had made Martin so amusing -- and launched her stardom -- was the style in which she sang it, garbed in fur, revealing nothing, just using Porter's witty words and her own beguiling smile. Cher was encouraged to play it -- garbed, with suggestive gestures and pointed leering.

Why wasn't someone around to correct this and many another recreation?

There were several outrageous gaps. Because, presumably, TV audiences wouldn't be interested in seeing the creators whose imaginations had produced such sine-quan on as words and music, writer Tom Eyen and composter Maury Yeston never got on the air for their "Dreamgirls" and "Nine" contributions. Is all this related to the current drive to force the Dramatists' Guild to lower royalty fees for the very people without whose ideas none of the productions would exist? Where would Tony night be without them? But home audiences never glimpsed them.

The Tonycasts have been bounced from one of the three commercial networks to another, with ratings the major desideratum to assure continuation. Through an arrangement with the original Tony creator, the American Theater Wing, the League of New York Theaters has assigned the Tony producing role to Alexander M. Cohen and his wife, writer Hildy Parks, an arrangement with several years still to run.

This season the Cohens did have tough challenges, for it had been the most fallow in memory. For a Tony show to start off with an excerpt from "Pump Boys and Dinettes" reflects to what depths Broadway stages have sunk.

Other choices might have been made: scenes from the few distinguished plays, accents not on TV but on theater. Tony Randall's running character of a critic had possibilities but was used only for those wisecracks theater people say they object to from the critics but then go and quote anyway.

By aiming for TV's lowest common denominator, the Tonycast and the theater it seeks to promote are both losers.