SANTA MONICA, Calif. (AP) _ Actress Heather Thomas, whose legs were broken when she was hit by a car, will require further surgery, hospital officials said.

Miss Thomas was in stable condition today after undergoing six hours of orthopedic and plastic surgery on her legs Thursday, St. John's Hospital said.

''Her physician, Dr. Steve Hoefflin, remains hopeful of a good prognosis,'' the hospital said in a statement issued Thursday. Her orthopedic surgeon, Dr. Kevin Ehrhart, said she will require additional surgery, but a decision on when it should be performed won't be made until Saturday.

Miss Thomas, co-star of the canceled ABC-TV series ''The Fall Guy,'' was walking across San Vicente Boulevard outside crosswalks after emerging from a market with a friend at 5:40 p.m. Tuesday.

She was struck by a car traveling 15 mph to 20 mph, police said. Neither Miss Thomas nor the car driver was cited.