ART

Andrew Wyeth’s long-hidden pictures of mystery model Helga went on display for the first time Sunday at the National Gallery of Art in an exhibition described as “sweet enough to please and salty enough to tease.� Between 800,000 and 1 million people are expected to see the Helga show during its four-month engagement, before it embarks on a cross-country tour of six cities until September, 1989.