The sets of "Diner" "American Graffiti" and "The Last Picture Show" have all come to life in Harvard Square, only this time in technicolor. With red and purple banquettes brightly splotched walls and yellow-and-blue checked floors the newly opened Johnny's is truly a blast from the past. While most students have yet to discover the Area's newest tribute to nostalgia--complete with a jukebox and bendy straws--the elusive locals are coming out of the woodwork to get a taste of Johnny's solid American fare.

The macaroni and cheese ($6.95) successfully updates the old standard with three kinds of cheese, and while the Egg salad sandwich ($5.25) is somewhat dry, the thin, skin-still-on french fries ($2.25) combine crispiness and tenderness to perfection. The frappes ($3.50) and ice cream sodas ($2.95) both made with Herrell's ice cream, are sublime. Johnny's extensive menu also features wide varieties of salads ($3.25-8.25) and egg dishes ($4.25-8.95) and they serve their pancakes and french toast ($5.25-6.25) all day.

Though perhaps somewhat overpriced for its genre, the thoroughly unsophisticated Johnny's Luncheonette provides a welcome alternative to the) (also overpriced and even greasier) Greenhouse Cafe and Mr. Bartley's. If you're going to create mundane fare you might as well do it well. Johnny's does. JOHNNY'S LUNCHEONETTE.

1105 Mass Ave., next to L'il Peach. 495-0055. Sunday to Thursday, 8 a.m. to 10 p.m., Friday and Saturday, 8 a.m. to 11 p.m. Take-out available.