Miss Piggy was a little embarrassed as it was, standing there in her plunging gown on the corner of M and Wisconsin.But then, oh heavens, the flower vendor kissed her snout. If it hadn't been plastic, it would have flashed several shades of porcine pink.

"I just came out," said the shy Miss Piggy, who was actually Larry Hack, a publicity administrator for a clothing company. But pretty soon, Miss Piggy got brave. "Isn't anyone going to buy me a corsage?" she asked.

From Georgetown to downtown, Washingtonians abandoned their wingtips, panty hose and qualms last night, trading them in for a chance to be pig for a day. A legal secretary emerged as a Playboy bunny; David Brinkley's aide turned up as a youth for Nixon, and the shah of Iran rode through the streets of Georgetown in a fat gray limo.

"Halloween," said Michael O'Hara, owner of the disco Tramps, "is the ultimate escape."

Take the Jolly Green Giant, for instance, who was ordering a spinach salad at the bar in Flaps Rickenbacker's on 19th Street. "It's just nice to be someone else for a while," she said. "It's a chance to act crazy and nobody cares."

The there was Sherlock Holmes across the street at the Appletree.

"You wanna know the truth?" he said, chomping on his pipe as the pickup scene progressed apace. "I'm dressed like this because weird people like him and him and her walk up to me and talk to me when ordinarily they wouldn't. It's a cheap trick for meeting people."

The secretaries and lawyers started first last night, turning up as butterflies, bags of jelly beans and mad hatters at their 19th-and-M after work watering holes. A devil, who is usually a chef, greeted guests at Flaps. "I am here to offer you all the pleasures of sin and corruption and booze," he said.

Much later, gays lined up as drag queens, nurses and Glinda the Good Witch at Lost & Found near Capitol Hill. There, rules of "No Males in Female Attire" and "No Females in Male Attire" were suspended for the evening. "Tonight's special," said the doorman.

But the real party was in Georgetown, the traditional scene for gays, straights, in-betweens, college kids, mothers, fathers and tourists to parade from bar to bar and beer to beer.

And although this scene pales considerably in comparison with the Halloween spectacle on San Francisco's Polk Street it is nonetheless an up-and-coming Washington institution that has caught on steadily in the last decade.

Georgetown bar people who've watched it say the hippies, who were really called that in 1968, started it all. The Generation is merely enlarging on it.

"Everybody goes berserk," said Ron Sullivan, the manager of Marshall's West End. "It's like a Mardi Gras in Georgetown."

Not that anybody was actually dancing in the streets. But close, Santa Claus, for instance, rang chimes in front of Roy Rogers on 19th; a nasty-looking skeleton pounced on innocent young things outside the Crazy Horse Saloon, and a pleasant man with a bloody, dripping eye asked for Visine.

"Well, I'm basically sick," he said, explaining why someone would appear in public with an eye that not only sat in his left cheek but also had an optic nerve springing from it.

Just a few doors up from the dripping eye were the potato heads -- five of them, from assorted Maryland suburbs.

"Georgetown is wild," said potato head No. 1, Murray Haje from Anne Arundel Community College. "Georgetown is the only place that's ready for potato heads."

"You ain't nobody unless you've been to Georgetown," said potato head No. 2, who declined to indentify himself further.

"Shut up, potato head," said potato head No. 1.

Meanwhile, outside a store full of nubby turtlenecks, a young woman who probably doesn't allow passes before the third date yelled "wanna pet?" at passers-by. On her dress, she wore a button that said the same thing. A friend standing with her wore a large protuberance under the bustle of her dress which made her look, well, generally undesirable.

Brinkley's aide, Julie Chrisco, who was hanging out with this strange company, wore bobby socks, a Peter Pan collar, a Nixon/Agnew button and newscaster Brinkley's glasses. She also giggled a lot.

The best place to stand to view the Halloween scenery was at any of the four corners of Wisconsin and M. A good five minutes would get you porn kings, werewolves, and assortment of goblins and at least one snake charmer.

Earlier, the snake charmer had sipped Grand Marnier and orange juice at the bar Rumors. Upon demand, he would remove a baby boa constrictor from a sweet little wicker basket.

Recoiling in terror, he insisted, wasn't necessary. "But if you were a mouse, you'd be in a lot of trouble," he said. A Marboro Man standing nearby agreed.

Not everyone wore costumes; a lot of people came as themselves to gawk Like five preppies from Choate who were in town on a three-day field trip.

"This is radical," said John Kremer, who wore a crew-neck sweater. "It's great."

"Georgetown University seems to be a microcosm of the greater macrocosm of Washington," said Dudley Lamont who, because he is a senior, apparently must say such things.

As Lamont was speaking, the good witch Glinda was absorbing the scene at Lost & Found. "For gays," said Glinda, who was really hairdresser David Byers, "it's a chance to get out a lot of the things you've been wanting to do all year."

And what one Lost & Found patron wanted to do all year was dress in a pink Qiana evening gown. Once this was accomplished, however, the problems began.

"They're drooping," he said, looking down. "I didn't wear a bra. And my shoes are killing me."