WHEN I WAS a kid, in the summer of '51, I almost frizzled my brain by cover-to-cover reading of The Official Encyclopedia of Baseball. And I would have lost my teeth if my mother had let me chew all the Bowman bubblegum I bought in search of a Joe DiMaggio card.

Now that I'm a big kid, I still have a voracious appetite for sports books and still collect baseball cards. There are those who would say this is evidence that the frizzling took, but at least I'm no longer obsessed with finding that Joe DiMaggio baseball card (there was no Joe DiMaggio card in 1951, his last season).

The Yankee Clipper was included, however, in the rare 1948 Leaf Gum Co. set, which I know because it said so in a copy of The Sport Americana Baseball Card Alphabetical Checklist by Dr. James Beckett and Dennis W. Eckes ($8.95) that I thumbed through at Sports Books Etc. in Springfield. I also scouted The Baseball Encyclopedia, now in its sixth edition, which when published by MacMillan in 1969 rendered even the updated Official Encyclopedia hopelessly obsolete.

Now I have my own copy of the baseball card checklist book (I already had the MacMillan). And there are dozens of others at SB Etc. that I would like to buy, too. How many others it's hard to say, because it's impossible to examine all of the titles in a couple of visits. There are more than 3,000 of them, according to owner Paul Haas, who says that even the chains stock no more than 400 sports titles.

Haas, who opened the shop in June 1984, says his is the country's only book store devoted exclusively to sports. While more than 400 titles are on baseball, when Haas says he stocks all sports, he is not kidding. Take soccer, for instance. The Washington area's countless youth soccer coaches would be wise to start their preparation here. How about Coaching Youth Soccer by Neil B. Ingels Jr. $8.95, one of about 80 soccer books Haas has.

"Maybe 5 percent of baseball books might be on playing and coaching, but soccer is just the opposite," says Haas. "Only 5 percent are spectator books, the rest are on playing and coaching." Many coaching books are texts, usually available only in college book stores.

Baseball, football, basketball, hockey and soccer are the top five sellers, says Haas. "Martial arts are a middle-level seller," he says. His diverse stock includes almost a dozen books on billiards, scores on bodybuilding and weightlifting, many choices on bicycling and backpacking, racquetball and wrestling, roller skating and skiing. His catalogue (he's getting into the mail-order business) lists 77 categories and includes fiction.

Besides books, Haas can special-order computer games and stocks table-top games, and carries sports calendars, posters, every magazine he can find and, of course, books and periodicals on collecting.

It's a great place for the sports freak to spend part of a Saturday afternoon. Leaving the rest of the day to shop for old baseball cards. Where? There are a bunch of places in the Washington area, and they don't sell just baseball cards. They've got football, basketball and hockey cards; baseball magazines and yearbooks; football and baseball guides; plus sports memorabilia and in some cases comic books, coins or used books.

Most shops have complete sets of baseball cards every year back into the '70s and thousands of single cards of superstars and obscure utility infielders back into the '50s. Inventory is less inclusive for gum issues of the '30s, candy cards from the '20s, cigarette cards from the teens and 19th-century sets, although several shops (particularly Collector's World in Gaithersburg and Golden Eagle Coin Exchange in Adelphi), could charge admission as museums if they had the counter space to display all of their stock.

One that could not is Den's Collectors Den in Laurel, which is not open on weekends, and sells relatively few cards, mostly reprints. Ninety-five percent of owner Denny Eckes' business is in selling plastic loose-leaf sheets for displaying cards and in publishing the books everybody has come to depend on for setting prices. Such as the previously mentioned baseball card alphabetical checklist, The Sport Americana Baseball Card Price Guide, a checklist-and-price guide on football, hockey, basketball and boxing cards, and similar books on team baseball checklists, baseball address lists (for autograph collectors), baseball memorabilia and non-sports cards.

Other local shops all have a wide range of cards. Gerhardt's World in Arlington (which includes Jeff Doranz's Baseball Corner) features a wall where traders can display cards in a weekly auction and is particularly strong on memorabilia, as is A.J's in Vienna. House of Cards in Wheaton and Barnett's in Springfield are particularly hospitable to youngsters. Golden Eagle, on the other hand, has a buzzer lock and deals primarily with dealers and hard- core collectors. Collector's Choice in Laurel is heavily into old comics.

The following list includes the stores' regular hours; it's best to call ahead during the holidays, when hours may vary.

A.J's SPORT STOP, INC. -- 255 Maple Ave. West, Vienna (behind the parking lot next to the Marco Polo restaurant). Contact John McNeely and Andy Reading. 938-1688. Monday-Saturday 10 to 7, Sunday noon to 6.

BARNETT'S SPORTS CARDS -- 6835-A Backlick Rd., Springfield (in arcade between Drug Fair and Safeway). Contact Tom Ravelette. 455-0145. Monday-Saturday 11 to 6, Sunday noon to 5.

COLLECTOR'S CHOICE -- Laurel Center, Route 1 Laurel (behind Horn & Horn, midway between Jamesway and the cinema). Contact Greg Brumfield. 725-0887. Monday- Friday noon to 8, Saturday 10 to 8.

COLLECTOR'S WORLD -- Quince Orchard Plaza, 612 Quince Orchard Rd., Gaithersburg (west from Route 124 -- Darnestown exit of I-270). Contact Jack Byrd. 840-0520. Monday-Saturday 10:30 to 8, Sunday 11 to 5.

DEN'S COLLECTORS DEN -- Laureldale Business Center, 8574 Laureldale Drive, Laurel (off Route 198 east of town). Contact Denny Eckes. 776-3900. Hours: Monday and Wednesday-Friday noon to 6.

GERHARDT'S WORLD -- (with Jeff Doranz's Baseball Corner), 2727 Wilson Blvd., Arlington. Contact Leroy Gerhardt and Jeff Doranz. 524-8640. Monday-Wednesday 11 to 5, Thursday and Friday 11 to 9, Saturday 11 to 6.

GOLDEN EAGLE COIN EXCHANGE -- 9119-A Riggs Rd., Adelphi (in Metzerott shopping center at intersection with Adelphi Road). 439-1444. Contact Bob Mangels. 439-1445. Monday-Saturday 10 to 6.

HOUSE OF CARDS -- 2406 University Blvd., Wheaton. Contact Steve Terman and Bill Huggins. 933-0355. Tuesday-Friday 11 to 7:30, Saturday 11 to 6, Sunday 11 to 4.

SACKS ARE LOADED -- Burke Center Plaza, 5741 Burke Center Parkway, Burke (in Burke Used Books store). Contact Barry Sacks. 250-1749. Monday-Tuesday and Thursday-Friday 3 to 8, Saturday 10 to 6, Sunday noon to 5.

SPORTS BOOKS ETC. -- 7073 Brookfield Plaza, Springfield (on Backlick Road near the post office). 451-1884. Contact Paul Haas. Tuesday, Wednesday and Saturday 11 to 5, Monday, Thursday and Friday 11 to 8.