AS A FULLY MATURE 38-year-old with bills to pay, Tom Ravellette should have overcome his obsession with baseball cards long ago. Instead, it has overcome him.

Ravellette walked into Barnett's Sports Cards shop in Springfield two years ago looking to add to his collection of several million bubblegum cards. This month, he hopes to wrap up negotiations that will allow him to purchase the store.

"I started collecting when I was eight years old and just never stopped," says Ravellette, who will display his wares along with 50 other dealers this weekend at the Baseball Card and Sports Memorabilia Show at Armory Place in Silver Spring. While a number of sports are represented by the cards -- football, basketball, hockey and boxing, to name a few -- baseball cards are easily the most popular.

"Unfortunately, a lot of the people who are getting into the hobby these days are not kids, or kids at heart," says Ravellette. "They are adults with big money who turn baseball cards into a business. But I just like the cards."

While most card collectors do approach the hobby as an escape to simpler times, there is big money to be made in bubblegum cards. Ravellette, who estimates his own collection to be worth approximately $200,000, says all cards increase annually in value by a minimum of 10 percent. Bill Huggins, who is co- owner with Steve Terman of the House of Cards in Wheaton, likens baseball cards to money market accounts.

"Cards are really a pretty good investment," says Huggins, whose great-uncle, Miller Huggins, managed Babe Ruth and the New York Yankees in the 1920s. "A complete set of 700 cards that you bought for $20 in 1981 has already doubled in value. What bank can give you a return like that?"

While a player's ability often determines the value of his cards, events off the field can have an even greater impact. For instance, when a Honus Wagner card was issued in 1910 by the Sweet Caporal cigarette company, Wagner, a vehement nonsmoker, objected. The card was recalled, but the few in existence have been sold for as much as $25,000 apiece.

Topps, now the largest baseball card manufacturer in the world, has also produced some valuable cards. When the second set of its 1952 cards failed to sell well, the company dumped its leftover cards in the water off New York City. As a result, the 200 cards in that set became scarce, with Mickey Mantle cards topping the price list at $3,000.

"There has never been a Topps card which didn't go up in value," says Dennis Eckes, owner of Den's Collectors Den in Laurel.

Some cards are valuable for bizarre reasons. When Willard Hershberger, a back-up catcher for the Cincinnati Reds, killed himself in 1941, his bubblegum worth took a grisly rise. Conversely, several dealers have said that the card value of players mentioned in the recent baseball drug trials has dropped sharply. And Huggins reports that Joe Theismann cards took a nose- dive following his messy divorce recently.

"I got mothers coming in the store who forbade their kids to buy cards of Theismann," says Huggins. "They thought he was a bad example."

What a player does once he retires can also up his card worth. Cards of Bob Uecker ("The worst player to ever play the game," says Huggins) now bring $5 because of his popular beer commercials, and cards of Joe Garagiola (now a sportscaster), Chuck Connors (actor) and even Jack Kemp (politician) are worth several dollars more because of their second careers.

Many current players have high card value based solely upon performance, including Pete Rose (as much as $350 for his 1963 rookie card), George Brett ($25), Eddie Murray ($21) and Jim Rice ($20). Cards of New York Mets' ace Dwight Gooden command $10 in New York.

Locally, cards of the Baltimore Orioles and defunct Washington Senators sell briskly, and former Washington Redskins quarterback Sonny Jurgensen's rookie card brings $18. But dealers say such sales are largely sentimental and confined to this area.

There are even signs that baseball cards have grown beyond the corner drugstore. One of the largest collections in the world is in the Metropolitan Museum of Art in New York City, and the Smithsonian Institution includes baseball cards in its "Nation of Nations" exhibit.

Warner Books has even published "Topps Baseball Cards -- The Complete Picture Collection," a massive, coffee-table tome that simply reprints all 21,500 cards that Topps has produced. The cost of the book is $79.95. The cost of the cards themselves is $23,099. The memories are priceless.

BASEBALL CARD AND SPORTS MEMORABILIA SHOW -- Saturday and Sunday, 10 a.m. to 6 p.m., Silver Spring Armory, Fenton Street and Wayne Avenue. Admission $2. For information, call 301/649- 7661, from 6 p.m. on. BASEBALL CARD STORES

If you'd like to be able to browse year-round, here are some stores to satisfy your cravings.

BARNETT'S SPORTS CARDS -- 6835 Backlick Road, Springfield, Va. 455-0145.

HOUSE OF CARDS -- 2406 University Boulevard, Wheaton, Md. 933-0355.

DEN'S COLLECTORS DEN -- 574 Laurel Dale Drive, Laurel, Md. 776-3900.