For a bond insurer like MBIA, a triple-A rating is worth pulling out all the stops to preserve.

Today the company announced plans to cut its stock dividend by 62 percent and raise $1 billion in new capital.

It is the second effort by MBIA to bolster its capital amid concerns that its exposure to collateralized debt obligations leaves it vulnerable to billions of dollars in mortgage-related losses. In early December, the private equity firm Warburg Pincus agreed to invest as much as $1 billion.

MBIA is reducing its dividend to 13 cents per share from 34 cents and is selling $1 billion of debt known as surplus notes that mature in 2033.

"Upon successful completion of its capital management plan, the company expects to meet or exceed the rating agencies' current capital requirements for MBIA to retain its triple-A ratings," MBIA said in a statement.

For bond insurers, a triple-A rating is the engine of their business. That rating provides a blanket of protection for states and municipalities that issue bonds, allowing them to pay a lower interest rate.

Fitch Ratings said in a statement that it expected to confirm MBIA's triple-A rating: "If MBIA successfully completes the offering at a level of $1 billion or higher, it will effectively address the existing capital deficiency per Fitch's modeling, and Fitch would expect to affirm all of MBIA's ratings."