IT'S PAST time for producers to bear down on their set designers. Priorities now are dominated by fund-raising, so why is there so much carelessness on how those funds are spent?

This season's most monstrous scenic waste was the layout Michael J. Hotopp and Paul de Pass designed for "Oh, Brother!," that ill-advised effort to improve on "The Boys From Syracuse," which stemmed, in turn, from "The Comedy of Errors."

As soon as the curtain rose on this relatively well-peopled musical, trouble glared at you. Representing the edge of a Middle East desert, the set suggested a hillock about eight feet high descending to the edge of theSee THEATER, 11, Col. 1 THEATER, From K1 stage. Carpeting of light buff was presumed to indicate sand. Only a strip of stage floor was uncarpeted, about 16 feet wide by, say, five feet deep. Thus, the performers in the ample Eisenhower Theater were limited to that downfront strip of playing area.

One should not have been too surprised, for Zev Bufman, the operating member of the five producers, also had employed the Hotopp-de Pass duo for his revivals of "Brigadoon" and "Oklahoma!" The chase scene of the former was decidedly awkward and, in the latter, "The Surrey with the Fringe on Top" looked like a presumptuous pony cart as it was forced to navigate down a narrow incline. In "The Little Foxes," honoring his high-class star, Elizabeth Taylor, Bufman did arrange for a substantial staircase, though its treads were barely wide enough for a size six shoe.

Another example of set-designer madness was New York's Circle in the Square revival of "Candida." Shaw was specific about his stage design, describing the Morrell home furnishings as "nothing useless or pretentious, money being too scarce in the house of an East End parson to be wasted on snobbish trimmings." Nonetheless, Kenneth Foy had arranged a garden that was quite chi-chi. This looked so perverse, I expected Beatrice Lillie to come on singing "There Are Fairies at the Bottom of Our Garden."

This fall the usually reliable Fred Voelpel proved careless. His set for "Einstein and the Polar Bear," the Hartford Stage Company discovery transferred to Broadway, represented a staircase and two rooms, the smaller a cluttered study with doorways leading off to a hallway and, I think, a back kitchen. But with the fourth wall removed, one never could be sure where the two rooms began and ended. Nor could Peter Strauss, Maureen Anderman and Company.

Such trivia can be absurdly distracting, taking one's mind from a playwright's presumably vital words. I recall spending the better part of a 1980 Act I wondering exactly how someone -- surely not the frail mistress of the house -- had gotten all those cups and plates so neatly arranged 15 feet above the kitchen floor.

I've been boggled by the architecture of a room that had two French doors opening onto a terrace, and a six-foot-wide fireplace between them. Judging from the dialogue, a room was right behind the hearth, but no walls could be glimpsed through the doors. What an intriguing wee hutch it must have been.

There was the case of the customarily brilliant Oliver Smith's design for "Do You Turn Somersaults?," the two-character Soviet drama Mary Martin and Anthony Quayle played in at the Eisenhower. What essentially needed no scenery at all was decked out on two revolving stages, requiring 18 instead of four stagehands.

In the New York production of "Sweeney Todd," Harold Prince decided against using Eugene Lee's design and, because he was locked into a timetable, bought an old glass-encased iron shell of a New England factory. It was broken up, trucked onto the huge Uris stage, upping the budget at least $600,000.

Expense apart, the major flaw in many designs is denial of performing space, crowding players into locked positions so that the designer can show off his vision.

That is exactly what set design should not do.

What should it do? A master, Robert Edmond Jones, explained: "The essence of stage setting lies in its incompleteness. It is charged with a sense of expectancy, and not until the actor has made his entrance does it become an organic whole."

The design, then, must serve the play, not the designer.

The craft is a relatively recent one. Until about 50 years ago, theaters had, instead, "scenic artists," who painted flats suggesting locale. David Belasco in America, Gordon Craig and Adolphe Appia in Europe, were critical forces who obliterated the flatness and would infuence such trailblazers as Jones, Lee Simonson and Jo Mielziner.

There are now some marvelous designers. Many got their earliest challenges at Arena Stage -- Robin Wagner, Karl Eigsti and Ming Cho Lee among them. With its square shape and tiered seats on all sides, Arena posed novel challenges; the floor and upper ceiling have been used creatively to define atmosphere.

The Timothy O'Brien-Tazeena Firth design for the National's "Evita" is marvelously spare, using a single door to suggest Evita's rise to riches and a balcony on which, from two perspectives, we see the public and hidden aspects of Peronist high life. Here is an example of the director, Harold Prince, working intimately with the designers.

There's a compelling return to life of the Brooklyn Dodgers' old ballpark in New York's new musical about Jackie Robinson, "The First," with David Chapman's steel fencing and its accompanying signs taking us effectively into the Dodgers' past. Another evocative New York scene is Ben Edwards' set for "The West Side Waltz," with a recognizable skyline glimpse of the ancient Ansonia Hotel, so vital to the neighborhood Ernest Thompson created for Katharine Hepburn and Dorothy Loudon.

David Hayes came up with an economic solution for the local changes of Edward Sheehan's "Kingdoms" at the Eisenhower, but something was lacking. An experienced star (not in the cast) explained my vague dissatisfaction. "The panels are effective, but the black backgrounds do them in. It's very boring to look at black." Also, with Paul Gallo's lighting design, too many lines came from the darkness.

For the first American production of Du rrenmatt's "The Physicists," John Bury's original London design was used. In the revival, starting previews Thursday at the Eisenhower, William Ritman has the design assignment. Though only his sketch has been available during the rehearsal period and the set won't be moved in until next week, Ritman is a reliable artist whose work one can anticipate with some confidence.

Du rrenmatt's design for a villa turned into a mental sanatorium is precisely specified, and Ritman's settings have served actors well from the time of his off-Broadway bow with "Zoo Story" and "Krapp's Last Tape." He had an arresting triumph with "Tiny Alice," inspired by Edward Albee's mansion-within-a-mansion-within-a-mansion requirements. Ritman's Arena Stage assignments included "Moonchildren" and "Zalman or the Madness of Good," both allowing players vital space for movement.

But when set design goes wrong, it can defeat both play and players. There's one reliable rule of thumb producers often forget: Less is more.