Moody's Investors Service said it was lowering the senior debt rating of the Los Angeles-based banking company one notch from AA2 to AA3 and its subordinated debt rating from AA3 to A1. The rating firm said about $3.3 billion in securities are affected. Moody's said First Interstate's Prime-1 rating for commercial paper was unchanged. In downgrading First Interstate, Moody's cited "a high and rising level" of bad loans and loan charge-offs. The agency said problem assets are particularly high in some non-bank subsidiaries and in the company's banks in the financially-troubled Rocky Mountain region.