With the ECB not yet ready to take over the technical but highly political responsibility for rating sovereigns, the bank's policymakers also agreed more immediate ways to help Spain and its banks at their meeting on Thursday.

One source who requested anonymity said the bank would further soften the rules governing debt and mortgage-backed securities - collateral often put forward by Spain's banks, adding that fuller details would be published on Friday.

The discussions come as Spain braces for a downgrade from small ratings firm DBRS, which without a change in ECB rules would trigger an extra 5 percent penalty on Spanish government bonds when used to get ultra-cheap ECB funding.

ECB members have heavily criticised the actions of rating agencies during the euro zone crisis and have vowed to reduce reliance on their assessments.

Creating an internal central bank rating system would sidestep S&P and its peers but could be a political minefield for the bank.

"In the case that the ECB Governing Council decides this, it would reduce the widely criticised influence of Standard & Poor's, Moody's and Fitch," one euro zone central bank source who spoke on condition of anonymity said.

"On the other hand, this could also expand the shrinking pool of collateral which banks in troubled countries have available."

The ECB declined to comment.

The decision on more immediate changes to help funding-squeezed Spanish banks, such as expanding the range of debt-backed securities or government-backed bank bonds, comes at a crucial time.

Spain plans to recapitalise its banks with up to 100 billion euros from the euro zone bailout fund, and while the ECB wants to ensure banks are not strangled by a lack of funding, it also wants to avoid removing too much of the pressure now on Madrid.

Spanish banks are now among the biggest users of ECB funding. Madrid will publish an assessment of the health of its banking sector later on Thursday, with results expected to show there is around a 70 billion euro capital shortfall.

Banks have to submit bonds or other types of securities to the ECB as collateral if they want to access its liquidity. Throughout the crisis, collateral standards have been repeatedly reduced to ensure troubled banks retain the ability to refinance at the central bank.

But opposition - particularly from the Bundesbank - has been strong. The German central bank has argued that the dramatic loosening of the rules has increased the risk of lending to banks for the ECB and the national central banks. (for story click )

RATING REVOLUTION

It is still unclear what criteria the ECB would apply in the future if it ditches the use of rating agencies in the area of sovereign bonds.

One central bank source said there would continue to be a sliding scale of haircuts (charges) that would be applied to the different countries' bonds.

"It is clear that the ECB will continue to make reductions depending on the creditworthiness of the country whose bonds are submitted to it as security," said the insider.

It would be a bold move by the ECB. It would have to employ its own experts and design robust methodologies to assess states' creditworthiness while at the same time tread a delicate line that could further throw into question its political independence.

Another central bank official said it could start to take shape next year and be part of a wider coordination among major central banks including the Federal Reserve and Bank of England to reduce the power of rating agencies.

"We are not yet there operationally, but this (coordination between major central banks) may well be the medium term solution," he said.

"At this stage we are just discussing among ourselves the kind of methods we might use for our own internal assessment, so whether in the future we will really have a harmonised and convergent approach I think it is a bit too early to say.

"But even if we don't have full convergence we will have a situation where central banks will be more able to do the assessment internally rather than relying on rating agencies," he said.