Some people never get enough theater. Those aren't the people who attend the annual Dramathon at New Playwrights' Theatre. After all, how much more could anyone take in ten days than seventy-eight hours of plays and readings? Day after day the shows will go on, new productions by local playwrights like Harry Bagdasian, Madeleine Lundberg, Mark Stein, Tim Grundman, Ken Bloom, to name just a few hours' worth. Twenty-three plays are expected, in all, plus eight new radio plays that will be presented live over radio station WGMS (AM & FM) as a kind of branch of the Dramathon. Young theater buffs will not be forgotten, for Saturday, May 6 (10 a.m. to 2 p.m.) and two Sundays (May 7, 1 to 2 p.m.; May 14, 10 a.m. to noon), clowns and puppets and children's theater will have their turn. Dramathon 78. New Playwrights' Theater of Washington, 1742 Church St. NW. May 5, 8 p.m. to midnight; May and 7, 10 a.m. to midnight; May 8 - 12, 6 to 11:30 p.m.; May 13 and 14, 10 a.m. to midnight. Entire Dramathon, $25; daily tickets, $6; children, $2. For schedule and information call 232-1122.