WELCOME CONVENTIONEERS . . . Wingtips, cherry lips, pinstripes, pearls . . . party passes, highball glasses, carnations, cigars . . . "Hello My Name Is" badges . . . champagne bubbles . . . felt banners . . . hand pumping, back slapping, cheek-to-cheek, jitterbug . . . toothpicks in melon balls, hotdogs in bacon rolls . . . blond-in-the-vanilla-cake.

Conventions are as American as plastic forks, as colorful as Miami Beach post cards, as varied as Liberace's rhinestones. Eight hundred and forty-five of them drew about 750,000 delegates--religious broadcasters, concrete pipe fitters, gastrointestinal assistants, circus historians and others--to Washington last year, making it one of the country's top three convention cities behind Chicago and New York.

Frederick Kleisner, general manager of the Capital Hilton, believes Washington some day could be the American convention capital. "This city has great drawing potential," says Kleisner. "We've got accessibility, night life, shopping and sightseeing. There's no limit to what we could do."

Washington area conventions are already a billion-dollar business, according to Austin Kenny, executive vice president of the Washington Area Convention and Visitors Association. Upon completion of the $98 million Washington Convention Center, bounded by New York Avenue and Ninth, Eleventh, and H streets NW, Kenny anticipates an additional 300,000 delegates will dine and dance through Washington each year.

We know them by their wilted carnations, tassled hats and plastic nametags: workaday Americans far from home, in luggage-strewn lobbies searching for hotel message boards; on downtown sidewalks deciphering the Metro map; in drugstores foraging for aspirin and laxatives; in carpeted corridors tooting paper horns, switching door number plates or weaving piggyback through stackable ballroom chairs.

Local businessmen know a good customer when they see one. The average conventioneer spends $500 during a four-day visit. According to some estimates, each dollar spent by a convention delegate is spent again by caterers, merchants and others as many as five times, Kenny says. Many businesses vie for the delegates' dollar by trying to satisfy the peculiar requests that they sometimes make.

So you want a dancing fountain? A chorus line? A cake? No problem. But Vincent Molloy, president of Acme Caterers in Mt. Rainier, had to come up with three old-fashioned "orthopedic-style" barber chairs overnight. And Carl Longley, president of B & B Caterers, 7041 Blair Rd. NW, had to supply a group from Alaska with dinner entrees of Alaskan shrimp, caribou and reindeer, as well as three stuffed polar bears for "a little atmosphere."

Penny Cummings of Sheraton Washington Convention Services customized the Joint Conference on Medical Conventions last January.

"We set up the entire front lobby as a hospital," recalled Cummings. "Served Bloody Marys through intravenous bags; hired models in nurse uniforms to cart VIPs to their rooms in wheelchairs; displayed flowers in bedpans. And of course we played the theme song from "General Hospital" over the Muzak system. . . . We wanted to give them something they'd remember."

Conventioneers almost never forget. They remember conventions-gone-by when weather was beautiful, business was great and conventions were conventions. They remember Vegas in '76 ("The big one," says Risk and Insurance Management Society (RIMS) delegate Dick Hughes), or San Francisco in '81 ("Now that was something," recalled RIMS delegate Karl Giesmann; "A blowout," said another).

On the third morning of this year's RIMS Convention (April 18-23) at the Sheraton Washington, the London broker could remember only that Bob Hope was in the ballroom the night before, and that afterward there was a party with two bars, maybe three, and some guy singing "every song Barry Manilow had ever written." The broker sat in the lounge--styrofoam coffee cup on briefcase, blazer on lap, rings under eyes--head-in-hands hungover. His head felt "like a piano."

"Of course this is business," said fellow piano-head Michael McBride, slumped on a nearby couch. "Convention business."

Anyone who has donned a styrofoam boater can tell you real convention business is not crafting company policy in mammoth assembly halls or brainstorming in sound-proof seminar rooms. It's buying drinks for the house, gossiping at neighboring urinals and winning contracts in smoky suites. It's raw, sweaty contact with someone from Boise who knows what you mean when you tell him your loss trend is critical and your four-door LeBaron rides like a dream.

"Contacts, that's where the money is," said RIMS delegate J.B. Hurstin of Mobile, Ala., a self-described "high-roller kinda guy" sporting a pink carnation in his lapel. "The object is to spread your name around. E-x-p-o-s-u-r-e . . . that's the word."

And e-n-t-e-r-t-a-i-n-m-e-n-t.

"Entertainment is to convention business as fertilizer is to farming," said Kleisner. "Take any month of the year and you'll have a wide variety of conventions in this city, but one element common to all of them is entertainment."

Fez tassles bouncing, bow ties bobbing, hands waving, the delegates of The Ancient Egyptian, Arabic Order, Nobles of the Mystic Shrine Mid-Atlantic Convention (May 27-31) entertained to the thumping beat of a six-piece disco band in the Capital Hilton Ballroom. The women at the National Association Daughters of the American Revolution in the Capital Hilton (April 20-24) chatted corsage to corsage around tables lined with finger sandwiches, fried shrimp and escargots. The delegates at the Roller Skating Rink Operators Association Convention in the Sheraton Washington (May 2-7), according to one delegate, were entertained "just riding up and down the (Woodley Park Metro) escalator."

Conventioneers also entertain themselves in the corporate flea market commonly called the exhibit floor. The Sheraton Washington exhibit floor reflected the characters of three conventions:

* Pinstriped RIMS delegates swapped business cards, synchronized watches and traded morning-after tales over soft Muzak as silk-fitted women pressed pens, buttons, brochures and golf tees into idle hands.

* Rink operators in one-size-fits-all nylon caps shifted counterclockwise through rows of gumball, cotton candy and wheel washer machines as a game show voice announced door prizes: ". . . tw-e-e-e-e-nty gallons of Plasticoat 320 epoxy skating rink coating . . . t-e-e-e-e-n dozen dispensers of Uncle Charlie's Magic Oil . . ."

* Internatonal Wine and Food Society Convention (April 23-25) delegates were pursued by hard-selling vintners through a maze of wine racks. "Our corks will be the shape of pyramids and Queen Nefertiti's head," said Egyptian Vineyards exhibitor Mandouh Ismail, cornering a delegate between two potted palms. "And our bottles will be the shape of King Tut."

Behind the exhibit floor curtains, conventioneers gather in quiet seminar rooms ("breakout rooms" in conventionese) to discuss profound goals that often are encapsulated in some mildly inspiring convention theme like "All New In '82," the RIMS theme, or "Back To The Basics," this year's rink operators' slogan.

Many delegates agree that convention organizers have a tendency to pack daily seminar schedules too tightly (the RIMS schedule listed more than 100 seminars in four days). RIMS delegate Jim Wagar of Cranberry, N.J., managed to take a client to Dominique's Restaurant for lunch after the Acquisitions and Divestiture Seminar. Paul Gary, a rink owner from Somerset, Pa., slipped off to the zoo with his family after the Roller Hockey Workshop.

But for most delegates, the sights of Washington are seen only from a hotel window. Says Rink Operator Walter Carter, "You're in the hotel so much, you usually don't know whether it's day or night."

"They arrange it that way so we can't drink before seven-thirty," complained RIMS delegate Jim Wagar.

Joan Kiesel, the International Wine and Food Society Convention manager, heard her share of complaints on the final convention day. She rubbed her forehead as delegates filed into her office screaming about everything from floor space to room service.

Kiesel listened patiently, then covered her ears when a custodian sent a case of Vinifera Imports' best wine crashing to the floor.

"Conventions," she sighed, "are cultural events."