ALEXANDRIA MAYOR Charles E. Beatley Jr. has combined an old-fashioned notion about public transit with some creative marketing to deliver a bus treat for his town: free off- peak-hour rides on the city's "Dash" system for 13 days leading up to Christmas. From 10 a.m. to 2 p.m., riders are finding the fare boxes covered with little Santa Clauses and the trips free and unlimited along all four intracity routes. What's more, the tab for this is not being picked up by the government. Mayor Beatley and City Manager Douglas Harman worked out an arrangement with local businesses to underwrite the project.

They were able to interest the Landmark Shopping Center and 20 Old Town Alexandria stores and restaurants in sponsoring and promoting the idea. Students from T.C. Williams High School's Distributive Education Club have been helping by passing out flyers, doing passenger counts and other surveys as a school project. As you might guess, ridership data for the first seven days showed weekday daily increases of 10 percent, and Saturday and Sunday increases of 19 percent. The two Landmark routes have shown an overall increase of 35 percent during the period.

Not only is the free-fare system spreading the shopping rush over off-peak hours, says Mr. Beatley, but it also appears to be reducing automobile traffic; some would-be motorists are attracted enough to the "Dash . . . No Fuss . . . Holiday Bus on Us" promotion to leave their cars at home.

Not every jurisdiction in the region could adapt a system so easily or attractively, perhaps, but the local governments are all taking hard looks at bus services that would augment and complement the bus system now run by Metro. As they do this, they may wish to take a few cues from Alexandria, where, at least temporarily, no-fare is faring well.