Tomorrow's Monday, it must be classical.

At the noon hour each weekday, Western Plaza, at Pennsylvania Avenue between 13th and 14th Street, will be the scene of a free, summer-long arts and music festival. Organized by the Pennsylvania Avenue Development Corporation and supported by donations from a dozen local businesses, the lunchtime concerts, which start tomorrow, will be thematically organized: Mondays will focus on classical music, Thursdays on big bands, Fridays on dance and street theater. Tuesdays will be a mixed bag--mimes, jugglers, comedians, clowns and an occasional fashion show, while Wednesdays will feature jazz, bluegrass, country and barbershop quartets.

There have been occasional concerts at Western Plaza in the past, but never a program of this scope. "It's all part of our program to bring people back to the Avenue during the day as well as the weekends and evenings," says Henry A. Berliner, chairman of PADC. "It's an opportunity to get people out looking around them at their surroundings instead of simply coming to work and going to lunch with their friends. It brings them out on the Avenue to see the restored buildings, the shopping opportunities, the restaurants and the parks. It's just getting people in the habit of getting out to enjoy all the Avenue has to offer."