If you are not a U.S. citizen, but are lawfully present, you may still be able to get Medicare, depending on your circumstances.
Specifically, you will qualify for Medicare even if you are not a U.S. citizen if you qualify to receive or currently receive Social Security retirement benefits, Railroad Retirement Benefits (RRB), or Social Security Disability Insurance (SSDI). In any of these cases, you will qualify for premium-free Part A. You will owe a premium for Part B.