"We accepted your invitation to join you in your bedroom," said Austin Kiplinger, president of Kiplinger Washington Editors Inc., as he greeted Robert and Roberta Freer, the owners of Greenacre, beside a brand new, custom-made bed. Compliments--if only until the end of October--of the Women's Committee for the National Symphony Orchestra and their 11th annual Decorators' Show House.

"After all of this, everything that isn't tacked down or not part of the actual structure will go," said Robert Freer. "Unless Roberta does something. I'm afraid she has a list."

All of this was the gala cocktail and dinner party given by the Women's Committee, a chance for volunteers, friends and supporters of the NSO to raise some extra money and take an advance peek at the house--35 rooms, from the gentlemen's study to the French country tea room, and all decorated by area design firms.

"It's also a chance for us to have some fun after all the work," said Lita Harrison, chairman of the Preview Party Committee, which last year helped raise more than $210,000 for the NSO. "We don't cook or put up the tents, but we do work. I put down sod in the front yard just this afternoon."

But the real work--the work the NSO hopes the public will pay $7 each to see between Oct. 8 and Oct. 29--is the rooms themselves.

"I think it's one of the best show houses yet," said Milo Hoots, a local interior decorator who came to see what his fellow designers did to Greenacre, an early example of Chevy Chase architecture.

"The rooms flow more smoothly than last year," he added, referring to Hillandale, a show house he helped decorate. "Only one room was a shame and that was a very small room."

One small room, the music room, was a hit with the evening's star of the hour, NSO's music director, Mstislav Rostropovich, who made a brief, cheek-kissing dash through the downstairs.

"It's fantastic," said Rostropovich as he entered the gray-striped music room, decorated with, among other things, a seated five-foot curly haired doll (with flute in lap) and a small cello off to the corner. "Completely untuned," said Rostropovich as he tested the instrument. "The gentleman we rented it from was afraid of that," said Roberta Rosenbaum of the Besthesda Design Group, the decorators responsible for the music room.

But lurking behind all the rooms--the furniture, the knickknacks and even 9-year-old Elliott Freer's pup-tented bathtub--was the knowledge that it would all be gone in a month.

"It must be a terrible blow to move out and bring all your own furniture in," said Drue Webster, wife of FBI Director William Webster. "But it's a fabulous way to get your house cleaned up."