Close-up on Dana Ashbrook

With his boyish demeanor, mop of black hair, and credits as the teen sweetheart in the movies Girlfriend from Hell and Ghost Dad, lanky Dana Ashbrook could have spent years in cute semi-anonymity. Instead, fortune smiled and he won an avid following as a real creep: Twin Peaks' quarterback sneak Bobby Briggs. ''Working with David Lynch, rules go out the door,'' says Ashbrook. ''He really likes me to play it big.'' Then the 23-year-old, youngest child of a drama professor and a teacher in San Diego, slips into a funny parody of Bobby's grandiose emoting. But one of Ashbrook's own ideas turned out to be too flamboyant even for Lynch and company — ''I really wanted to shave my head on camera this season, but they vetoed that.'' With mane intact, he's looking forward to new story lines now that Laura Palmer's killer has been unmasked, and he tells viewers eager to learn about Bobby's own murderous past (alluded to in just one line in the series) to go look up Jennifer Lynch's The Secret Diary of Laura Palmer. ''I loved reading it,'' he says. ''It was about me.'' Nevertheless, Ashbrook, who otherwise plays harmonica and sings folk tunes in an L.A. coffeehouse band, isn't yet convinced the attention will last. ''We're hot now,'' he says, ''but I look at an episode of One Day at a Time and think, 'Whoa, those haircuts!' In five years we could be a nostalgia item.''