Standard & Poor's and Fitch Ratings may enable European Central Bank President Jean-Claude Trichet to support a private investor rollover of Greek debt by saying a default rating would be partial and temporary.

Trichet put Greece's fate in the hands of ratings companies when bank officials began saying in May that the ECB, which has lent 98 billion euros ($142 billion) to Greek banks, would refuse to accept the nation's bonds as collateral if any "burden sharing" by private investors produced a default rating. Growing support for a rollover helped push the yield on Greece's 2-year bond down 320 basis points to 26.2 percent since June 27.

Trichet and European political leaders have been at odds over creditors' role in a new Greek rescue after last year's 110 billion-euro bailout failed to stop the spread of the region's debt crisis. Germany backed down two weeks ago from its plan to extend maturities on existing Greek bonds. Now, it may be the ECB's turn to yield to rating companies' threats that a rollover would trigger default, or risk the collapse of Greek banks and spreading contagion.