Several members of the Los Angeles congressional delegation asked the federal government Tuesday to postpone moving hundreds of thousands of chronically ill seniors and disabled patients into managed care. In a letter signed by 14 U.S. representatives, the officials raised concerns about whether the health plans would be ready for the transition and whether patients would have access to the care they need. The state and the federal government signed an agreement in March establishing the program for the "dual eligible" patients, who receive both Medicare and Medi-Cal. About 450,000 patients, including 200,000 in Los Angeles County, are expected to be enrolled in the program.