WASHINGTON (AP) - As a precaution against Year 2000 computer problems, the post office and banks will receive January Social Security checks and electronic files for direct-deposit benefits a day earlier than usual. The 44 million elderly and disabled Americans who collect Social Security benefits should expect to get their money on time, said Social Security Commissioner Kenneth S. Apfel. For most people, that's Jan. 3. "So many Americans rely on Social Security for that benefit," said Apfel. "We had to be there, and I believe we are." Social Security transferred to the Treasury Department late Tuesday the last of the necessary Y2K-compliant files for electronic payments through bank accounts. From Treasury, they will go, through the Federal Reserve, to banks across the country by Dec. 30, a day earlier than usual, to ensure on-time posting of direct deposits to individuals' accounts.