The agency said no change was likely now on the top-grade Aaa rating of UBS or on Credit Suisse's Aa3 rating as a result of what it called "the historical legacy of a past generation of bankers".

Moody's said it had assessed the financial implications of settlement negotiations on distribution of dormant Holocaust-era accounts to survivors and heirs. A committee chaired by former Federal Reserve chairman Paul Volcker is auditing the claims and Jewish groups say several hundred million dollars could be at stake.

Moody's said it expected the Volcker Committee audit to be substantially completed by the end of the year and noted that the two banks had agreed to pay the amount determined by the committee.

"The financial costs of a settlement -- as well as the costs associated withthe banks' pledge to pay the amount of dormant accounts determined by the Volcker Committee -- are also difficult to project...but these should be manageable," it said.

Moody's said the threat of boycotts in the United States added an element of uncertainty.

The Swiss government and the banks last month urged US cities and states to think carefully about imposing boycotts threatened against banks over the issue. UBS and Credit Suisse said they had shown good faith in trying to settle claims. "The direct financial costs associated with such potential sanctions are unlikely to be severe relative to the banks' earnings strengths and ample capital positions," Moody's said.