The fourth set of quadruplets born in the Los Angeles in less than a year were delivered by Caesarean section at Northridge Hospital in the San Fernando Valley. The two boys and two girls, born Sunday about 10 1/2 weeks prematurely, were doing fine in the hospital's neo-natal care unit, their doctor said, as was their mother, Bridget Lach, 31. But the father, Bill Lach, was suffering from high blood pressure. "His blood pressure shot up so much he had to be put on disability," Dr. Arnold Bresky, who delivered the quadruplets, said. Bill Lach, 36, of Van Nuys, said he has had to take extended medical leave from his job as a research assistant at Hughes Aircraft. The infants were named Kenneth Charles, Matthew Evan, Kathryn Bryn and Rachel Claire. The babies are expected to remain at the hospital two to three months. Doctors said Bridget Lach was taking a fertility drug to induce pregnancy.