THEY HAVE NAMES like Sonic Junkyard, Rockpower Records, Annapolis Oldies, Mad Doctor's Records and Intergalactic Garage. On a handful of weekends a year, these basement-terprises meet and blend into a kind of hot wax stew, a Vinyl Event, a Record Convergence, a Vinyl Meet; generically, a record convention.

Those who have experienced one will tell you it makes shopping for music at the mall positively anemic.

This weekend, the Washington-Baltimore area hosts two record get-togethers, including a record convention at the Holiday Inn in Crystal City.

How does a vinyl gathering differ from the neighborhood record store? Chances are in every way -- selection, price, atmosphere and salesmanship.

Walk into a record convention and you're immediately struck by the wide variety of non-record material on display -- books, magazines, paperbacks, photographs, posters, TV and movie nostalgia items, buttons, jewelry, pennants, T-shirts -- all jammed in nooks and crannies not taken up by hundreds and hundreds of boxes of records. The merchandise is only as limited as the vendors' imaginations, which is to say, unlimited. And recent shows have given high-tech its due by offering for sale both compact discs and live concert videotapes.

Perhaps most characteristic of conventions is their chameleon-like ability to reflect the musical preoccupation of the moment. At last summer's shows, most vendors' tables screamed "Bruce!," displaying an overabundance of Springsteen paraphernalia. January's Vinyl Event, on the other hand, was something of a merchandising tribute to rock and roller Rick Nelson, who was killed in an airplane accident in Texas on New Year's Eve. The convention, coming less than two weeks after the singer's death, featured dozens of vintage Nelson items for sale -- LPs, photos, magazine covers and 45s with original color sleeves -- all assembled with an efficiency and haste that would make K-Tel Records, those masters of musical dispatch, green with envy.

And at a recent two-day Record Convergence at Tysons Corner, vendors came prepared to satisfy an unusually high demand for albums by Peter, Paul and Mary, an interest no doubt sparked by the group's 25th aniversary performance at the Kennedy Center the same week.

The real difference in a record convention, though, is not sales, but salesmanship. At a record show, merchants and consumers of every musical taste, from punk to opera, blues to bluegrass, Rolling Stones to 101 Strings, converge to intellectualize about, pan over, hype, put down, nurture and dismiss out of hand both good old sounds and slick new sounds. Today's conventions are the musical equivalent going to a "Star Trek" convention before "Star Trek" went Hollywood.

Consider these slices of conventin life:

At a recent show, vendor Bud Newman from Arlington wore a button to broadcast his musical bias: "Back to Mono." Newman, a record collector since 1971 and a convention regular, specializes in top 100 chart merchandise. He rails against what he describes as "mindless robotics" in current music and becomes defensive about the threat to vinyl from new technologies. "I don't think CDs will replace the memories these records represent," he says. While he considers record shows his "mutant hobby," his wife, Wendy, jokingly calls it a "sickness" and claims she would happily trade his convention habit for some less obsessive pastime, "like alcohol or other women."

At the other end of the hall, vendor Jeff West, a six-year convention veteran from New York City, is doing brisk business in a new-fangled medium, compact discs that he "brought along on a hunch." West prices his CDs at a reasonable $10. He refers to their vinyl counterparts as "museum pieces."

Wearing a T-shirt that says "I'm not here, I'm in Europe," Michael Simmons of New York City, an editor at National Lampoon and a movie-music fan, discovers, after some brisk table hopping, a sealed copy of the soundtrack to the 1962 Stanley Kubrick film "Lolita," Price: an unstiff $12, less than half the price a used copy would fetch in NYC, if, Simmons, indicates, a copy could be found. He looked for five years before landing it at Virginia's Record Convergence.

A musical SOS goes out over the house PA system: Does anyone have any early album by English folk guitarist Roy Harper? A vendor from the far end of the hall shouts back in the affirmative and another successful musical linkup between vendor and consumer is made.

Some vendors, like Pat Allen of Reston, are content to deal strictly in non-record items. Allen hawks musical memories, specializing in mementos of the King of Rock and Roll and convention staple, Elvis Presley. She started with antiques and worked her way four years ago into rock and roll collectibles: an Elvis 1977 memorial coin ($4); Elvis arcade vending machine cards (75 cents each); and an Official Elvis Fan Club pen ($5.95) -- tip it and Elvis floats past the Graceland gates.

While Elvis commands his king's share of Allen's table space, the Beatles also make a strong showing: a John Lennon AM table radio with "1940-1980" printed across its face ($23); Beatles hair brush ($15.95); an 8-inch plaster George Harrison bobbing head doll ($40 -- although Allen points out it's listed in a Beatles collectors book for $60); and a TWA flight bag with the caption, "The Beatles to the USA," which Allen says she picked up from a dealer in London.

Barry Alpert of Silver Spring began selling music-related merchandise at rare book and jazz shows in New York City in 1979. He specializes in obscure paper items, "unknown paper," he calls it, from out-of-print books, paperbacks and magazines that celebrate the fringes of the rock and roll and jazz scenes.

Alpert hovers over his table wearing a fiery red T-shirt proclaiming, "Ezra Pound Centennial" under an English prof's corduroy sports coat. The image he strikes is Berkeley and the Free Speech Movement.

While Alpert says his merchandise reflects his "natural avant-garde taste," the collective appeal is clearly '60s nostalgia: first-edition hardbound copies of John Lennon's "A Spaniard in the Works" ($59.99) and "In His Own Write" ($29.99), as well as manager Brian Epstein's book on the evolution of the Beatles, "A Cellarful of Noise" ($45). Nearby are two-decade-old hardbound copies of "Superstar" by Viva and "The Autobiography and Sex Life of Andy Warhol," as well as racks of racy vintage paperbacks by "beat generation" writers Jack Kerouac and William Burroughs, figures from a literary epoch that evolved long before most of the convention's patrons were born.

TIMETABLE OF TURNTABLE EVENTS

Here's a list of coming local record conventions:

RECORD CONVENTION -- Saturday, National Airport Holiday Inn, Crystal City. 9 to 4:30. $2. 317/747-7360 for dealer inquiries only. RECORD CONVENTION -- Sunday, Quality Inn, Towson, Md. (exit 26 south from I-695). 9 to 4:30. $2. 317/747- 7360, dealer inquiries. RECORD MART VI -- April 13, Annapolis Guard Armory, Willow Avenue & Hudson Street, Annapolis. 10 to 6. $2. 301/229-5385. GREATER BALTIMORE COLLECTORS MART III -- June 29, National Guard Armory, 610 Reisterstown Road, Pikesville, Md. 10 to 6. $2. More than 200 table of collectibles, about 30 percent of which are records. 301/229-5385.