Los Angeles County health officials reopened a three-quarter-mile stretch of Will Rogers State Beach closed since Friday because of a sewage spill in Pacific Palisades. The county lifted the restriction after tests showed that organic waste in the surf from Temescal Canyon north to Sunset Point had dropped to safe levels, said Dick Rinaldi, director of environmental protection. A tree root ruptured a sewer line last Wednesday. The state Water Quality Control Board in Los Angeles will consider penalties against the city after receiving a report on the rupture. The water board could fine the city a maximum of $10,000 for each day of the spill, said Richard Harris, the board's assistant executive officer.