Rescue plans for troubled bond insurers

All eyes are on Wall Street's troubled bond insurance companies as they struggle to salvage their top-notch credit ratings and avert a broader financial crisis.

Credit-rating provider Standard & Poor's on Monday ended its downgrade review for MBIA Inc's top "AAA" rating, citing success by the largest U.S. bond insurer in raising new capital. The "AAA" ratings of Ambac Financial Group , the second largest insurer, were affirmed but remain on review for a downgrade.

The bond insurers, which guarantee payments on some $2.4 trillion of debt, are facing billions of dollars of expected losses from guarantees on risky subprime mortgage bonds.

Investors are spooked by potential rating downgrades because they could trigger a wave of forced selling of bonds the insurers have guaranteed, prompting more losses for Wall Street banks and lifting borrowing costs for consumers and city governments.