"BYE, BYE," says the sign on the door.

"Last day of business Saturday . . . Fixtures and equipment for sale."

After 129 years, Brentano's is fading from the scene, a victim of cut-rate competition and economic bad times. The bookstore chain's branches at 1326 F St. NW and 5508 Wisconsin Ave. in Chevy Chase will close this evening. Two other area branches, Prince George's and Seven Corners, will remain open for the time being. The main, Fifth Avenue Brentano's in New York is being offered for sale in the wake of bankruptcy reorganization proceedings filed last May.

At Chevy Chase yesterday, six customers roamed the front end of the cavernous store, where the last few hundred books and magazines were concentrated. Behind them ranged yards and yards of empty shelves and racks.

"We had a sale at 25 percent off," said manager Theresa Ridge, "and then two weeks later it was 50 percent off, and then a week ago Tuesday we had 70 percent off. Boy, we had a crowd in here then!"

The same thing happened downtown: Each new sale announcement brought a crushing wave of buyers who snapped up the dictionaries and art books and guides and nonfiction and games and gifts.

Hardback fiction went last, it seems.

Still on the shelves: "The Beverly Hills Diet," Fodor's guide to Belgium and Luxembourg, "Who Killed Karen Silkwood?," the last volume of Proust's "Remembrance of Things Past," five books on how to solve Rubik's Cube, a Mary Stewart omnibus, an Ian Fleming omnibus, "101 Uses for a Dead Cube," John Jakes, Gordon Liddy, Simenon, Melville and Shakespeare.

Side by side: "Crisis Investing" and "How to Prosper in the Coming Good Years."

There were a few 1982 diaries and astrology guides, a big 1983 Snoopy calendar and an almost historic 1981 desk calendar filler. Also a game called Conquest with the notation, "Returned and exchanged--missing one piece."

Browsers stuck close to the paperbacks and magazines, which included back numbers of Oui, Washingtonian, Life, Reader's Digest and Inside Sports. Nobody seemed to be interested in the gifts across the aisle (plaster, life-size eggplant and asparagus bunch, $34 the pair) or the handful of earrings still in their display case.

These last are a sore point with Brentano's veterans.

"It was the economy, of course -- thanks a lot, Mr. Reagan -- and Crown Books didn't help," commented Ridge, "but the problem mostly was upper-management strategy. We'd been telling them for ages to phase out the nonbooks."

For years, Brentano's has been something more than a bookshop, its "cultural department stores" featuring original paintings and art reproductions, jewelry, games, gifts and novelties. The chain thrived here, its first Washington branch, which opened in 1884, becoming famous as "the bookstore of the presidents."

Theodore Roosevelt was the first president to buy a book there. Its name is lost to history.

Eventually there were 10 stores in the area, including a museum shop in Georgetown. In 1962 the chain founded by August Brentano, an Austrian immigrant who began it all with a newsstand in a New York hotel, was sold to Crowell-Collier Publishing. In August 1981 it was sold to a group of investors headed by Paul L. Ohran of New York. As of last May there were 28 branches across the country.

Behind the front counter at Chevy Chase, Virginia Hamilton sold a couple of magazines to a delighted customer for 60 cents. Hamilton has been with Brentano's 17 years and used to manage the Silver Spring branch.

"I was here when this store opened 12 years ago," she said. "It was Nov. 1, and we had Erich Segal here signing books. We've had a lot of authors. Judith Viorst was my favorite; she was in and out of here several times. Melvyn Douglas came in once, William Manchester, Montgomery Clift's brother . . ."

The staff used to number well over a dozen, but now there are only seven, unemployed as of 6 tonight.

At the downtown branch they were talking of a beer party.

Mused Hamilton: "We used to have Discount Books up the street, and we got along with them fine. But then Crown came in and Discount closed. You'll find there's a Crown Books right close to all our stores."

Crown, a spinoff of Dart Drugs, has changed the whole genteel world of bookselling with its aggressive discounting and concentration on current hits.

A customer asked about the spotlights in the ceiling. Oh yes, they're for sale, he was told. Would he like to put in a bid?

On a greeting card rack, a small drawing of two alligators embracing.

"Let's not say goodbye . . ." reads the caption. And inside: ". . . let's just say, 'See you later, alligator.' "