On Friday nights this winter, as many as 150 teenagers take to the ice at the Mount Vernon RECenter's rink, gliding and sliding as a deejay spins the latest hits from the pop, rock and hip-hop charts.

The students shell out admission and skating fees, but they are not the only ones paying. Fairfax County is paying, too -- for the right to play the music. Throughout the county, at community centers and special events, the music people hear is often copyrighted. That means it isn't free.

Prodded by the American Society of Composers, Authors and Publishers (ASCAP), the county Board of Supervisors took the matter so seriously that it recently agreed to a new, blanket licensing agreement with the society. The agreement simplifies the previous rules on how the county government pays royalties for the right to use copyrighted music at local facilities and events.

Not much money is at stake; Fairfax's annual fee comes to about $6,400. But to ASCAP, an important principle is involved. Recognized by the federal government as a performing arts society, ASCAP is responsible for collecting royalties for performances of copyrighted music. The group in turn forwards the fees to the people who hold the individual copyrights.

Up to now, each county agency, such as the Park Authority, was responsible for its own royalty payments to ASCAP and the paperwork that went along with it. Those payments totaled $5,000 to $7,000 a year. The new agreement -- adopted by other local governments nationwide -- eliminates the cumbersome practice of individual agencies paying separate licensing fees. Instead, the county will pay a single fee covering all departments and agencies.

The $6,400 charged to Fairfax is based in part on its population of more than a million people. The county would pay additional fees to ASCAP for music played at any county-sponsored event that generated revenue above $25,000.

If the county had kept the old agreement, ASCAP said it would not issue any new licenses for future facilities. That would have meant that users of the soon-to-be-completed West County RECenter would have been limited to hearing music that is not copyrighted. And exercising to "The Old Grey Mare," for many people, ain't what it used to be.