By day she is chief of the Writing and Editing Unit of the Federal Deposit Insurance Corp., dutifully supervising a group of seven in the production of such computer manuals as "Bank Information Tracking Systems." But when she jumps on the Metro home to Vienna, she starts plot- ting, because by night she is Terryl L. Paiste, playwright.

"I recommend eavesdropping on the Metro for playwrights who want to sharpen their ear for dialogue," she says. Apparently it works. Since 1979, eight of her plays have been produced around the country, and even in the Soviet Union, at the Young Spectators Theater in Irkutsk.

This year theaters in Ashland, Ore., Hartford, Los Angeles and D.C. (Source The- atre) staged her comedy "Dumb Stuff" -- "a thinly veiled reminiscence of the time my friend Linda Shaw and I weasled our way onto Johnny Carson's old show 'Who Do You Trust?' in 1961, the year we graduated from high school. We won $250. It was the major achievement of my teenage life." Her current project is "a philatelic comedy-drama-murder mystery dedicated to my husband, the stamp collector."

This summer she was among 17 area writers chosen for a five-day TV comedy writing workshop sponsored by Warner Bros. and the Maryland Film Commission. Afterward, participants sent completed scripts to Los Angeles for evaluation. The goal is to end up with a sample script that can be used to solicit scriptwriting assignments.

Paiste says her script is for CBS's "Designing Women," but she won't say more: "One of the things they told us at the workshop was never tell anyone about your script or show anyone your script because everyone in the TV business is a thief."