WASHINGTON — The Trump administration is freezing payments under an Obamacare program that protects insurers with sicker patients from financial losses, a move expected to add to premium increases next year. At stake are billions in payments to insurers with sicker customers. The latest administration action could disrupt the Affordable Care Act, the health care law that has withstood President Donald Trump’s efforts to completely repeal it. In a weekend announcement, the Centers for Medicare and Medicaid Services said the administration is acting because of conflicting court ruling in lawsuits filed by some smaller insurers who question whether they are being fairly treated under the program. The so-called “risk adjustment” program takes payments from insurers with healthier customers and redistributes that money to companies with sicker enrollees.