THE KENNEDY CENTER'S new Terrace Theater serves both as a performance stage and a recital hall. It also serves as a reprieve from the common catchup elegance of its host building.

It is rose, mauve and matte silver -- and uncommonly elegant.

The new theater was designed by Philip Johnson, who needs no introduction at this point in Time, having recently been portrayed on that magazine's cover, grimly clutching his latest baby, the model of his ornately roofed AT&T building.

Johnson and his partner John Burgee usually give star performances only. At the Terrace they were supported by a cast of no fewer than six star consultants, led by Dr. Cyril M. Harris, leading master of the art, science and gamble of creating auditoria with good acoustics. The other five consultants worked on lighting and rigging, audio/visual, structural, stage and mechanical engineering -- skills which, in this unusually flexible performance hall, are even more sorely needed than in ordinary theater design.

"The architect," says my trusted 1902 edition of Sturgis' "Dictionary of Architecture and Building," "cannot be said to have anything to do with the interior of a theater," except decorating the auditorium walls and proscenium arch and leaving the theatrical engineers and machinist alone to work their magic.

But this is not true in this case. Johnson/Burgee obviously stage directed their ensemble of magicians so as to forge their various parts and performances into a harmonious, totally integrated whole.

While elsewhere, for instance, exceptionally good acoustics have been achieved only with conspicuous acoustical devices (such as the ugly baffles at the Minneapolis Concert Hall), here Dr. Harris' forms are an integral and pleasing part of the total design.

While elsewhere spotlights usually spoil the most dramatic intentions of the interior designer, worse even than the unsightly but vital "exit" signs, the Terrace conceals the lighting in attractive ceiling undulations that bounce the sound the way Harris wants them to bounce.

During the year and a half that Johnson/Burgee worked on the design of the Terrace, they must often have thought of Walter Gropius' famous "Totales Theater" project of 1926. Gropius and stage director Erwin Piscator had set themselves the task to design a theater capable of every conceivable dramatic illusion. I am sure it would have been terrible, if it had actually been built. Multi-purpose buildings usually serve no purpose really well.

But it seems to be different here, despite what Total Theater demands Roger L. Stevens and Thaomas R. Kendrick, director of operations, made of their architects.

First, there was the technical feat of building a theater with 513 seats as a penthouse on top of an existing building. Every brick, panel and piece of machinery had to be brought up above the Eisenhower Theater by freight elevator. The Turner Construction Co., which did the hauling and building, can take a bow for that.

Then there are the acoustic demands of a recital hall for chamber music, small orchestra and solo musicians, which are successfully accommodated only by special architectural configurations and rreatments.

Drama and musical comedy, on the other hand, what with good sight lines and deep stages (the death of sound), require entirely different architectural configurations and treatments.

To combine the two, the Terrace has, to begin with, a steeply sloped auditorium much as in the great outdoor theaters of antiquity. You may get acrophobia walking down to the front seats, but even in the uppermost seats you are close enough to the stage to see and hear well. Besides, the steps are lit at all times.

The auditorium is perfectly square without balconies or galleries. The seats are mauve and comfortable. The rose walls are lined with plaster half columns, painted matte silver -- some-what Art Deco, but pleasantly unobtrusive, almost neutral.

The proscenium opening is large -- 35 feet by 18 feet -- and the stage is deep for all manner of scenery, scrims and what have you. There is an orchestra pit for 30 to 35 musicians, which can be raised to stage level, adding a thrust stage, or to floor level, adding 38 more seats.

The trick by which the performance stage is converted into a recital hall is performed by the iron curtain, or fire curtain. It is set behind the proscenium arch and faced with wood. When lowered, it keeps the recital sound where it ought to be -- in the auditorium.

The Terrace Theater is meant as a part of the educational and experimental search and research program Roger Stevens has been dreaming about all along to make the Kennedy Center truly a center of the performing arts, rather than a festival hall. Other parts of this dream are the present Musical Theater Lab as well as the soon to be opened Performing Arts Library.

But it may well be that the Terrace Theater turns out to be more than a study hall -- something like the intimate theaters big cities used to have, which served connoisseurs rather than broad audiences. They were primarily places for art, rather than only entertainment.

Whether the new theater works as well as it looks, I dare not predict.

If it does, it will make an important contribution to the history of theater architecture.