Advertising - like tha Redskins' offense - has all but disappeared from RFK Stadium this season.

The dearth of billboards is deliberate, says Bob Sigholtz, general manager of what people are supposed to start calling Starplex, for STadium ARmory ComPlex.

This season's ad revenue - Sigholtz won't say how much they might be - were sacrificed to get ready for a unfield advertising program at the stadium.

Ultimately, the signs will be back, he says, along with what is being promoted as the world's greatest scoreboard, complete with animated color cartoons and singing commercials.

The super scoreboard, he estimates, will cost $1.2 million. Advertising fees will buy it, and once paid for the sign will make money, says Sigholtz.

The D.C. Armory Board is with-holding approval of the scoreboard until it gets an auditor's report verifying that rhe project can be handled without cost to the board or the taxpayers.

The Armory Board's track record on self-supporting projects is not good. The stadium was supposed to pay for itself. But it hasn't been able to pay the interest on its $20 million in bonds since the first year and never has paid a dime on the principle. It's now assumed the city and the federal government will be stuck for the tab when the bonds fall due next year.

Sigholtz says he doesn't know how big annual advertising revenues will have to be to pay off the principal and interest on million-dollar scoreboard.

The sign he wants would be the world's first color, animated football scoreboard. The nearest thing to it is the sign in New York's Times Square put up by American Sign and Indicator Co., which is likely to be the only bidder on the RFK job.

Next to the computer-controlled scoreboards will be four giant advertising panels: the companies that buy them also will get two minutes of commercials on the animated scoreboard at each game.

Sigholtz said Starplex is asking major advertising agencies to bid on handling the whole business - scoreboard, billboards and posters.

Until this year, three different agencies sold stadium advertising: one had posters, another billboards, and so on. All three contracts wree allowed to lapse so a unified contract could be worked out, but the deal wasn't completed in time and that's why a giant sign for the Diplomats soccer team and a smaller one for The Washington Post are the only ads there.

DISCO WINNER: Michael O'Harro, who turned the little-used dining room at Georgestown's Carriage House restaurant into the super successful Tramps discoteque, has been named Disco Businessman of the Year. For the second year in a row.

It's the kind of honor that raises all sorts of questions - like who picks the disco businessman of the year? The answer is Billboard magazine, the outfit that makes money musically. It not only picks disco songs, it runs & disco convention and sells a how-succeed-in-disco book.

And how do you get to be disco businessman of the year? Well, being in bed with Billboard, professionally speaking, doesn't seem to hurt. O'Harro, it turns out, is not only a consultant to Billboard, he wrote its disco book.

And the book, of course, is being promoted as the work of the disco businessman of the year . . .

Self grandisement is not a sin to disco promoter O'Harro, it's a way of life. After spending a long lunch hour telling a reporter about himself. O'Harro follows up professionally with a note saying. "I hope you are as excited about the story as I am."

Oh, the pluck of the Irish.

WHERE ELSE?: If Tramps is the oldest disco in town, the newest soon will be opening in the sprawling downtown basement of the Atlanta Building at 930 F Street.

Paul Parsons, who paid upwards of $2 million for that structure and the one next door at 928, has cleaned 90 years of cobwebs and crud out of the lower level to create an entertainment complex.

It's to be known as Underground Atlantis, which is redundant.

At any rate, by the first of the year there will be disco dancing live entertainment and fine food downstairs.

MORE STORES: Washington's reputation as the hottest retail market in the country continues to be enhanced by new stores, new branches of old ones, and expansion. Among the latest:

Home Inc., the do-it-yourself floor covering chain opened its eight unit, in Seabrook. Since 1974, it has doubled the number of stores.

Wm. Fox Co. has added a second-floor women's clothing department to the men's store it has occupied at 2136 Pennsylvania Ave. since 1965. P. J. Bolle, fomerly of Pappagalo, is the manager.

Celtic Fair, a shop featuring Irish imports, opened in Alexandria's Old Town.

The new Springfield - Hilton - at I-95 and the Beltway - won't open until spring, but general manager Jack Daniel has set up temporary quarters in the nearby Executive Plaza building while the 250-room hotel is being completed.