Comes the revolution, curators at Hillwood won't be leading tours through the tokens of czarist opulence quite so blithely. "The wealth must have been incredible," says one, pointing to a gold chalice commissioned by Catherine the Great, and an Easter egg by Faberge, presented by Nicholas II to his mother in 1914. "Beautiful, isn't it?"

Brothers and sisters, workers of the world! Indeed the place is gorgeous. The Russian decorative art at Marjorie Merriweather Post's mansion is recognized as the finest outside the Soviet Union's own Hermitage museum. The French 18th-century furniture in the drawing room, rare tapestries, Sevres porcelain and Marie Antoinette's desk and chairs are equally impressive. But can any museum in Washington get away with charging $7 admission (or even $2 for the 25-acre grounds alone) when worthwhile freebies abound?

Hillwood can and does. July 6 marks Hillwood's fifth anniversary as a museum and, as usual, tours are booked weeks in advance. It's definitely a worthwile trip, after you've covered the city's populist exhibitions.

The "highlights" tour of the Versailles of Rock Creek Park takes 11/2 hours and is guaranteed to overwhelm. Catherine the Great's dinner dishes. A rug made for the Orlovs, another that belonged to Emperor Maximilian and a chandelier as big as the Ritz from Catherine the Great's bedroom. Passageways between rooms hold showcases of carved rare stones, glass and more delicate porcelain. The English library is subdued, with an imported marble mantlepiece, Waterford crystal chandelier and Scottish snuff mulls in ram's horns and stag's hooves, polished and mounted in silver.

A cabinet in ebony, ormolu (gilt bronze) and lapis lazuli is nearly lost in the Icon Room. In the front hall there's a Louis XV traveling jewel chest decorated with more ormolu. "The only problem with ormolu," says the guide, "is that many workers died of mercury poisoning."

An unfortunate detail. To keep Mrs. Post and her Washington pied a terre running took 26 gardeners, 77 crewmen on the yacht, three pilots on the "Merriweather" airplane and 36 assorted others. The Smithsonian had to give up Hillwood in 1976, after three years of financial drain. Insurance premiums for the jewels and art treasures were $15 million a year; it was expected to cost about $475,000 a year to maintain the estate, about $700,000 annually to operate it as a museum. To each according to its need.

The Post Toasties heiress began her collection in the late 1930s while living in Russia with her third husband, Ambassador Joseph E. Davies. She spent only four months a year at Hillwood, from 1955 until her death in 1973. The real estate, valued at more than $5.4 million, includes exquisite gardens, a greenhouse, dacha (one-room adaptation of a Russian country house) and an exhibit in homage to her father, C.W. Post, founder of the Postum Cereal Company of Battle Creek, Michigan.

The grounds tour, a relative bargain at $2, begins with azeleas lining the drive to the portico, and progresses to tulips, pansies, camellias and flowering trees surrounding the mansion. A Japanese garden, a French garden, a rose garden and "rhododendron walk" make for an unusual backyard. There's a clear view of the Washington Monument six miles to the south.

Gus Modig, conservator of Hillwood, was head butler for 15 years. He supervised an inside staff of 36, making sure the cook had the right menu. He still puts fresh flowers in the vases throughout the 35 rooms every day -- "always orchids in Mrs. Post's bedroom and dressing room" -- and changes the dining room table settings once a month.

"We wore a tuxedo in the daytime and full dress for dinner," he says. A taste of "Upstairs/Downstairs"? "That was just television," he demurs. His quarters have become a gift shop.

An informal poll by tour guides shows the public's favorite room is the breakfast nook, off the endless formal dining room, overlooking the gardens. While it has a glass- and-ormolu chandelier from a Russian palace, it's on a small-enough scale that hoi polloi wouldn't feel ridiculous eating Post Grape Nuts there. DROOLING AT HILLWOOD Tours (limited to 25 people, and the minimum age is 12) are given Mondays and Wednesdays through Saturdays at 9, 10:30, noon and 1:30. Reservations are required; call 686-5807. Admission $7. Special tours are offered on Faberge, icons, porcelain, Russian ecclesiastical and French decorative art, and small containers. Gardens-only tours, $2, 11 to 4, also require reservations. From downtown, go north on Connecticut Avenue, right on Tilden Street, left on Linnean Avenue, 11/2 blocks to the gates at 4155.