Among the "Secrets" in October's 25th-anniversary edition of Washingtonian magazine are "The City's Greatest Mysteries," the handy "25 Secrets You Can Use" and the tongue-sticking-out "Places You Can't Go." Not among the secrets divulged in the issue, which will be unveiled at tonight's quiet office birthday party, is "How We Choose Covers."

Not to worry. Jack Limpert, the resourceful man who has edited Washingtonian under both of its owners for the past 21 of its 25 years, sat down at his old Royal manual last summer and typed up just such a list of inside secrets, secrets he's happy to share. These "thoughts on covers," as he calls them, are based on his analysis of the monthly's best and worst covers over the past decade or so -- another promising feature, incidentally.

The precepts range from the self-evident -- "The idea has to be of broad interest" -- to the axiomatic -- "A good idea can be hurt by a bad visual treatment, but not much can be done visually to salvage a bad idea." The magazine's experience is that "Politics doesn't sell" -- figures, doesn't it? -- and that "Women sell better than men" -- although contrary to cynical opinion, Washingtonian steers clear of all but the chastest cheesecake.

"Scandal sells better than sociology," Limpert has discovered; yet, perversely, "Positive sells better than negative." Sports fans, ponder this: "Redskins sell. Other sports subjects don't." (The John Thompson cover last March is the year's worst-selling issue to date; a Joe Theismann cover from 1987 is the second-best-selling cover of all.)

Among the really bad cover choices, for reasons of idea if not visual treatment, were "The New Legitimacy of Hypnosis," "Fantasies: If You Could Be Someone Else" and "Jack Kemp -- the JFK of the '80s" (oh, well). Other famous Washington personalities who left newsstand buyers cold are Marion Barry, Edward Kennedy, Dillon Ripley and Robert Bauman.

One further secret Limpert discovered five years ago, when Washingtonian published a 20th-birthday issue that did not hurry from the newsstand: "Anniversaries don't sell." So this year, instead of looking back at the city through the magazine (as its competitors Regardie's and Washington Dossier did this year in their 10th- and 15th-anniversary issues, respectively), Washingtonian came up with another guiding shtick altogether. The whole issue, fronted by its computer-generated silver "SECRETS," is a photo-driven, superlative-crazed, classic Washingtonian insider guide to the city: service as entertainment, or vice versa -- every city magazine's yin and yang in yeasty harmony.

Such dash and flash as Washingtonian so energetically radiates in every issue does not, oddly enough, characterize the people who put the magazine out.

Not Limpert, goodness knows. A tall, inscrutable drink of water from Wisconsin, by seniority and stature he is the William Shawn or Helen Gurley Brown of city magazines. Limpert is a question-asker and list-maker, as unopinionated as you please, still "fascinated" after all these years on the job (he's only 56) by "the most complicated city in the world." Rudy Maxa, one of his gossip columnists, calls Limpert a "great voyeur," meaning no prurience (well, maybe a little).

The other study in non-glitter is Philip Merrill, the Annapolis Capital newspaper publisher who bought the Washingtonian 11 years ago from its patrician founder, Laughlin Phillips. Philip and Eleanor Merrill, though plenty aggressive and plenty opinionated, have shown little interest in using their perch as a Washington dinner party entree (or as a chance to play editors, either). The male Merrill now spends most of his time in Brussels, where he recently became assistant secretary general of NATO.

The party tonight could be some swell and limo'd soiree in one of the city's many canape zones, but instead it's just a small gathering amid the desks and file cabinets, just the gang and a senator or two. The anniversary check ($100,000) goes not to Ridgewell's but to 25 children's charities.

The 316-page October behemoth does not much resemble the skinny and self-conscious little monthly that made its debut in 1965. The Washingtonian (the "the" has fallen away) of that day -- with its watercolor of the Supreme Court on a silent cover -- had all the innocent pretenses of its surroundings. It read like the work of the upper-class, New Yorker-bred clique that owned and wrote it, and it spoke for all the appropriate liberal aspirations of its age -- racial harmony, museums and highways, irony, the endless weekend. Washington was on the brink of being Athens.

Today Washingtonian is a more confident and less quirky presence -- a middle-aged distraction from all that is not Athens around us. As it grew and prospered, the magazine learned how to indulge the sophisticated appetites of its clientele -- once predominantly District of Columbia residents (and white ones at that), and now predominantly Maryland and Virginia residents (ditto). Washington's aspiration was relief from its real estate prices, back pains and a tireless inferiority complex, and Washingtonian has doggedly provided it.

The magazine's informal creed is to help its readers live better and to help them better understand the place where they live. The issues that sell best at the newsstand and checkout line (and Washingtonian sells an impressive 70,000 of its 170,000 monthly press run to such impulse buyers) are the ones whose covers people have come to associate with this genre of magazine: 50 best restaurants, 52 dream weekends, annual best-and-worst. With such a Pavlovian reader response, it is hard to blame the editors for ringing the bell so often.

Though many do. In a recent City Paper jeremiad against the city magazine, "Washingtedious," Editor Jack Shafer declared that the the August issue (with the Barbara Bush look-alike on the cover) had "all the excitement and immediacy of an in-flight magazine. Make that Air Canada's in-flight magazine." He pilloried Washingtonian's "arthritic walks down memory lane," its popular annual spread (or "inane feature") on houses of Washington celebrities, its cheerful profiles, its relentless scorecards (this one on the Bush Cabinet).

Dyspeptic as Shafer can get, he is describing the very elements that seem to have inspired its readers' loyalty. Brian Kelly, the editor of Regardie's, Washingtonian's most serious local competitor, compares the magazine to a public utility.

"Every major city has to have one, and Washingtonian is as good as any city magazine in the country. But the problem with being a public utility is that you have to deliver the same thing month in and month out." Asked if that isn't what its readers want and appreciate, Kelly replied that the magazine "tends to underestimate its readers in terms of surprising them or provoking them with stories." Holding the franchise, he said, means "doing more serious journalism than they do."

That may be, but Washingtonian is not nearly as unserious as it looks. Financial health has enabled Limpert to pay, and high demographics have enabled him to attract, Washington journalists of national reputation to the magazine's pages and even its masthead -- Jack Germond and Jules Witcover, Fred Barnes, Robert Samuelson, Vic Gold, Nick Kotz, Diana McLellan and Michael Kinsley. One of its former editors, Lynne Cheney, now chairs the National Endowment for the Humanities. The Smithsonian Resident Associate Program, whose last magazine showcase brought New Yorker editors for a season of speakers, this fall is honoring Washingtonian with its sponsorship.

Through the years Limpert has sneaked into the evanescent and utilitarian mix stories of journalistic moment -- National Magazine Award-winning ones, for a fact: about the surgery performed on Ronald Reagan in the hours after he was shot, about the state of U.S. military leadership, about emergency medical care, about the big 1987 train wreck in Essex, Md., and, just last year, about an extraordinary surgeon's apprentice. One of the recent cover stories, and one that dared to fare badly on the newsstand, was Barbara Matusow's report on the unfulfilled promise of racial integration in Washington.

These stories occupy the serious side of Limpert's editorial equation. He says he is sensitive to striking the right froth-and-fundament balance, not just inside every issue but from month to month on the covers. Best-and-worst and restaurant covers meet short-term demand, in his view, but the less popular covers and stories build "long-term respect for the magazine" -- the kind of subliminal and not-so-subliminal feeling that will motivate a subscriber to renew a subscription instead of thinking, nah, it's nothing but lists and junk.

Washingtonian's subscription renewal rate is excellent -- 85 percent -- and because the cost of direct mail to find new subscribers is so high, the renewals represent a high operating efficiency. Advertising in Washingtonian is likewise exceptionally good -- the monthly had more ad pages than any other city magazine last year. The magazine's reliance on local retail advertising has meant that its fortunes have closely tracked the local economy's -- ad pages are off 15 percent or more this year, after several years of virtual obesity.

The Merrills and Limpert are banking on the loyalty, and neediness, of their advertisers, who can't buy Washingtonian's creamy paying readers ($100,000 average income) at that price from other publications. Nor as many of them; the city magazine, for instance, outsells such premium titles as Smithsonian, Time, Sports Illustrated and Cosmopolitan in the Washington metropolitan area.

As for other local magazines that hanker for the same advertisers -- Regardie's, Dossier and Museum & Arts Washington -- they bear the burden (more noted inside the business than out) of being "controlled-circulation" publications. That means most are sent free of charge to correct addresses, and thus are considered different animals -- the difference between drop-ins, however welcome and presentable, and invited guests.

Washingtonian has survived and more, in the view of Maxa, because it has become a "validating" experience for its readers: It makes them feel good about the life they lead, and confirms their status in the community. But as the cult of money and self-indulgence seems finally to be cracking, the city magazine faces the challenge of reinventing itself -- for a younger readership than its fortyish average, to name one key consideration.

Just how Washingtonian plans to do that is a secret.