A writer previously under contract to Universal City Studios has sued the studio for using his work without payment or credit as the basis for the television series “Northern Exposure.”Sandy Veith, in a complaint filed in Los Angeles Superior Court, said he signed a contract to develop television projects for Universal in 1981 and the next year delivered a screenplay about a doctor whose medical schooling is financed by a small town in exchange for a promise to become the town doctor for a specified period. After several contract extensions, the suit said, Universal’s rights to exploit the screenplay expired on Dec. 31, 1987. During his contract negotiations with Universal, Veith said he was represented by Creative Artists Agency, another defendant in the suit. The agency later represented the creators of “Northern Exposure,” which was produced by Universal, the complaint said. Veith wants at least $ 2 million in compensatory damages and unspecified punitive damages.