Above the battlefield where Confederates whipped Yankees more than 100 years ago, an air war is being fought this week at Bull Run Regional Park.

The weapons are multicolored plastic discs, and they are being tossed, curved, caught and bounced in an effort to win their masters an invitation to the World Frisbee Championships this summer in New Jersey.

That's right campers, Frisbee is alive and well. If you thought they went the way of the Hula Hoop, you should catch the finals of this qualifying competition Friday and Saturday at the Park in Centreville.

"It's more than just a fad," insists Eric Simon, a 25-year-old computer programmer and member of the Washington Area Frisbee Club.

Simon is one of 139 Frisbee fanatics who spent the week competing in six events including distance throws, freestyle, golf and discathon, which is something like a marathon run-and-toss.

We're talking serious Frisbee now. Some of these folks came from as far away as California to compete. Jennifer Winsor, an 18- year-old college student from Philadelphia, for example, has her bathroom walls covered with plastic discs.

Ask them why they have remained loyal to a sport the rest of the world takes so casually and you hear passion.

"There is so much room for creativity and imagination," said 26-year-old Jens Velasquez, who has been to the World Championships for each of the last seven years. Jens and his 23-year-old brother Erwin say they make their living at the sport through sponsors and exhibitions.

Some say Frisbee throwing began (with pie tins) as early as the 1920s at Yale and Princeton. But it wasn't until the mid 1950s that Wham-O, the company that manufactured Hula Hoops, marketed what were then called Pluto's Platters. Since then, Wham-O says it has sold over 100 million of the plastic discs.

This week, during breaks between flings, the competitors talked about the hazards of their sport: Frisbee finger, Frisbee elbow and worse; Judy Horowitz, the current women's champ, once ran into a tree in the midst of the nationals, but carried on.

Horowitz, 20, passed up the nonstop partying of Vassar graduation week to defend her title. "It's like four years of school and I'm missing all the fun parts," she said. But if the sacrifice was bothering her, it didn't show.

EASTERN NAT'L FRISBEE CHAMPIONSHIPS -- Semifinals and finals will be held 8 to 6 Friday and Saturday at Bull Run Regional Park. For details, call 703/631-0550.