A Santa Barbara-based firm said it won Bankruptcy Court approval to buy Paramount Petroleum Corp., owner of a 46,500 barrel-per-day refinery in Paramount, for $43 million in a leveraged buyout. The purchaser is Alaska Pacific Refining Inc., formed two years ago to build a 120,000-barrel-a-day refinery in Valdez, Alaska. The refinery is in the engineering stage after President Reagan rebuffed attempts to block it on grounds that it would process Alaska crude oil for export. The Paramount refinery, which employs 170, produces gasoline, asphalt and other products for Southern California. No jobs will be lost, the new owners said.