There's never any knowing just where the great American play will turn up next, but for the past five years, the Actors Theatre of Louisville has been a good place to look. Every spring in the course of its Festival of New American Plays it turns its stage over to a handful of unproduced works, culled from thousands of entries, then invites critics, talent scouts and producers to see them, three a day, over a whirlwind weekend. Since that's how "The Gin Game" and "Crimes of the Heart" first came to national attention, something must be working.

"Write On!," the hour-long documentary about ATL's fifth festival, to be aired tonight at 9 on Channel 32 and at 10 on Channel 26, is a lively examination of artistic temperaments and some of the complexities they're up against. Occasionally, it tends to indulge in hype (one critic in the thrill of being interviewed describes the event unabashedly as "a miniature Cannes festival of theater"). But for the most part, the program is a reasonably informative blend of interviews and scenes. Among those on the talking end are ATL's producing director, Jon Jory, who prefers to view the festival as "a party given for the American playwright," and literary manager Elizabeth King, who admits candidly that of the unsolicited scripts ATL receives annually, only one in 1,000 is worthy of production. The scenes are from Wendy Kesselman's "My Sister in This House," Paul d'Andrea's "A Full-Length Portrait of America," Ken Jenkins' "Chug" and William Mastrosimone's "Extremities."

The latter, a particularly graphic play about a woman's revenge on her rapist, was the clear critical hit of the festival, and Mastrosimone, a soft-spoken gentleman with a pudding face, explains how he came to write it over 36 hours in a friend's basement. Now a Broadway production is planned, which lends even more justification to the comment of a play scout in ATL's lobby, "You always find something here."