The "sexiest thing on two legs" is how women colleagues describe a certain photographer at the National Geographic Society. So when he showed up at the society's 7th-floor Christmas/office party this year dressed as Olympic swimmer Mark Spitz, an auction was held for his bikini-clad body.

"Never let it be said," says a male partygoer who declined to bid, "that the old Geographic is a stuffy, staid organization."

The Goldberg/Marchesano ad agency, host of the hottest office party in local advertising circles, sent out sickly green invitations this year. "At this party," they promised, "alien"-style, "no one can hear you scream." They were right.

Dallas Northington, a downtown office building manager, has been to seven office parties in seven days. He still can't remember what he did Dec. 17.

"Building managers go to everything," he reports. By midweek, at the party for the National Bar Association, he was down to having a weak Scotch. A very weak Scotch.

Welcome to Christmas Office Party Season, that joyous time when the boss is out of the board room and into the eggnog. The time to whoop it up with the receptionist, imbibe in the marble corridors of the Justice Department, and, at a recent and raucous affair that shall go unnamed, watch porno flicks -- among them, "Debbie Does Dallas."

("the whole town?" asked one partygoer. "No," came the response , "just the team.")

But it's a time, too, for a few stale rumballs between 3 and 4 in the suite down the hall, for stiff Bloody Marys at the chairman's estate, for forced frivolity, for "Where have you been all my life?" and other lines that have lost a hell of a lot of subtlety in 12 months of practice.

"Like New Year's Eve," says a Washington psychotherapist, "there seems to be an enormous pressure to have a fantastic time. That's probably why people drink so much. It's also a fantasy time. There's a sense of letting go -- a sense that next year will be different."

Analysis aside, here are a few party highlights from this season's crop:

The Party as Punishment. Last year, the folks at the Bureau of Labor Statistics proved they're not as boring as people who fidget with numbers all day are supposed to be. In fact, they had 10 parties over three days. Loud music. The crash of glasses. Maybe even a lampshade or two.

This year: Lunch. One day, at their desks. All pushed together. And no amps.

"Someone's cooking a roast beef and someone's cooking a ham," says William Stead in the office of administrative management. "It's very restrictive, which is probably the way it should be. But I tend to be a Scrooge."

The Party as Songfest: White House press secretary Jody Powell, joined by Carter-Mondale campaign chairman Robert Strauss, finished off the Christmas party at the Los Angeles Times Washington bureau with a rousing rendition of "Amazing Grace."

Bob Devilin, the one-man band normally seen at 17th and Pennsylvania, provided the entertainment which, according to one source, also included "dancing in the aisles."

The Party as Cutback: Several years ago, the American Petroleum Institute people had caviar. This year, it was, alas, deviled eggs and anchovies. "We're cutting down," says R. G. Ensz, a media relations person who, for one, misses the old days.

Still, API did manage a small band, 400 people, and the Mayflower Hotel. And lots of highly acceptable behavior, even by office party standards.

"Wild sex?" says Ensz. "In a large room like that? With our president there? There was hardly any dancing, even."

Which brings up:

The Party as a Sit-Down, Civilized Affair: Not a whole lot of these, but you can find them if you look. Try psychiatrists. "Nobody gets bombed out of their mind or anything," discloses Elsie Fuller, assistant to the Chairman of Georgtown's psychiatry department.

What they do is have a nice, orderly dinner and cocktail hour in the Westchester Apartments dining room. Pleasant chitchat, about oh, the weather, and maybe a few patients. "Very somber," says Fuller.

Lawyers tend to be noiser. Or lawyers at Arnold & Porter, anyway, who host an annual do that comes under the heading:

The Party as Blow-Out: "It's not chintzy," says Stephanie Phillipps, an associate. Indeed it's not. Crabmeat, shrimp, turkey, roast beef. Four hundred people at the Internaional Club. Disco dancing. A skit that spoofs the partners.

And absolutely no spouses, although they were invited in previous years. (Depending on whom you talk to, the spouses made the party either too big or too boring. Probably a little of both).

So is there now a healthy consumption of holiday spirits? Replies partner Dan Lewis: "Goodness, no."

Other blow-outs, although a bit controlled, include one for Geico Insurance at their Western Avenue building and a formal dinner and dance for 1,900 hosted by the Riggs National Bank at the Sheraton-Park Hotel. The menu was filet mignon, with dancing 'til dawn. Well, 1 a.m. actually. After all, these are bankers.

And finally:

The Party as Fantasy: David Margolis, chief of the organized-crime section at the Justice Department, has discovered himself to be madly in love with the voice of Carol Parker, WMZQ-FM disc jockey. This year, he invited the voice to the office Christmas party.

"No business was discussed," he said. "Actually, we talked about what Carol Parker would look like."

But alas, she didn't show. Sighed Margolis: "I'll bounce back."