THE CRAZE for Elvis and the classic rock of the '50s and '60s has spread beyond the record stores and concert halls to nightclubs, including Studebaker's in Rockville and Flashbacks in Springfield.

Studebaker's, in the Days Inn on Rockville Pike, is part of a chain owned by the Louisville-based Fifties Corp. It uses a high-tech neon-and-tile recreation of a '50s diner to house an attractive nightspot. Studebaker's considers itself a club, and thus charges admission every night but Monday and restricts entrance to persons over 22. This keeps out the college crowd but doesn't cut the lines waiting to get in on weekends.

The entertainment is on several levels. The deejay plays continously, lip-synching the songs and changing masks and costumes (and toy instruments) to match the record. Every so often, the bartenders, waiters and waitresses join exultantly in a choreographed dance atop the tables and bars. The crowd at Studebaker's does its part, filling the large dance floor and the bars and counters, even on Monday nights.

The diner, with its two large bars, many island-counters and booths, is attractive and clean, with the flashy decor changing the atmosphere to that of a party rather than a singles bar.

In Springfield, Charley's Place has renovated the lounge, adding pictures of Marilyn Monroe and James Dean and other period pieces. A deejay plays hits of the golden days of rock every night and the waiters and waitresses have their own version of showtime when they join in and dance. Flashbacks is smaller than Studebaker's -- 114 seats compared to Studebaker's 450 -- and has a smaller dance floor. FLASHBACKS --

STUDEBAKER'S --

Now open Monday through Saturday, but will begin opening 11 to midnight on Sundays after Labor Day. Valet parking Tuesday through Saturday. $2 admission except on Monday. Age limit: 23 and older. No athletic footwear or sandals, cutoffs, faded or frayed jeans or T-shirts; in short, look neat and clean. The show begins at 8, after the all-you-can-eat happy hour. Lines on weekends. 881-7340.