Richard Sommerhalder, a convicted murderer, will not be paroled to Santa Cruz County where a petition movement against him was in progress, California Department of Corrections officials said Wednesday. Dist. Atty. Art Donner announced a drive Saturday to get petitions asking that Sommerhalder not be returned to the county and so far at least 7,000 signatures have been obtained. Donner said Sommerhalder, 39, was one of the most dangerous criminals ever produced by the county. He was convicted in 1977 of two murders and two rapes and has a long previous record.