Moody's Investors Service said the deal reached in Congress on the financial reform bill will not prompt it to immediately change its ratings on U.S. banks — but that action might come later.

The ratings agency said it must first discern the effects of the legislation on the profit banks make in the credit industry.

"Any rating actions that result from passage of legislation into law would be made following an assessment of the implications of the legislation," Moody's said.

The ratings service said the legislation includes both positive and negative elements for banks' stand-alone credit profiles.

"Clarity with regard to the law's content and an understanding of its likely implementation by regulators will be key to our ongoing analysis," said Robert Young, managing director for Moody's North American Bank Ratings.

Young said the willingness of regulators to use the new resolution authority granted in the bill will influence its views, but regulators' ability to use the authority will be restricted for some time.

"We are therefore still of the opinion that senior debt and deposit ratings of systemically important banks in the U.S. will continue to benefit from some unusual level of support until the economic recovery is sustained, financial market health is restored, and the risks of attempting to unwind an interconnected institution are reduced," added Young.