The ratings firm put almost the entire euro zone and some of its biggest banks, including Deutsche Bank, BNP Paribas, Societe Generale and UniCredit, on a downgrade warning this month.

In a telephone interview with Reuters on Friday, S&P's Managing Director of its Financial Institutions division, Scott Bugie, said this week's unprecedented injection of three-year loans by the ECB was a positive step.

But it would not solve the banks' key problem of carrying too much debt.

"The move in itself will not lead to any improvement in (banks') credit ratings," Bugie said.

"The operation is a big deal. It's half a trillion euros of three-year money at an ultra-low rate. It is not solving the fundamental issues though... It's kicking the can a long way down the road rather than just a little bit but in the end it is still kicking the big old can down the road."

While the ECB remains heavily reluctant to ramp up its purchases of troubled euro zone states' debt - a move many economists feel may be the only way to get to grips with the region's crisis - it has underscored its readiness to provide limitless funding to ensure banks do not go under.

Bugie said this week's move showed the ECB was committed to solving the crisis, and although it pushed the potentially problematic interlinkage between debt-laden banks and sovereigns to new levels, it provided some much needed breathing space.

"The ECB action doesn't change the fundamental picture but it does buy valuable time and it will be taken into account when we do our analysis to resolve the creditwatch actions.

"It deepens the symbiosis between the sovereigns and the banks, the passing of the risk back and forth. It also adds to the big question of how the governments and the central banks will exit."

S&P is not expected to release its eagerly awaited verdict until January on debt ratings for the 15 euro zone countries it placed on review, two independent European government sources told Reuters on Friday.

With the rating agency also currently having over half of Europe's banks on a negative outlook and many of those on what it calls its 'watch negative', meaning a near-term downgrade is likely, Bugie added that 2012 was set to be a turbulent year.

"We are looking for a rough ride in 2012, the first quarter will be very tough."

"For Italy it will really be a test (due to big sovereign issuance due)," he said.

(Reporting by Marc Jones; Editing by John Stonestreet)

• A Permanent Economic Emergency