NEW YORK (Bloomberg) - Ambac Financial Group Inc., the second-largest bond insurer, is determined to maintain its AAA credit rating and would consider reinsuring some of its assets to bolster capital, chief financial officer Sean Leonard said.

"We're going to defend the AAA credit rating," Mr. Leonard told a conference arranged by Bank of America Corp. in New York.

The company stopped buying back shares to help preserve capital, Leonard said. Rating companies will probably complete their reviews of the bond insurers in December, he said.

Moody's Investors Service, Fitch Ratings and Standard & Poor's have said they are examining the bond insurers to see if they have enough capital to support their AAA credit ratings after downgrades of securities that they guaranteed.

Both New York-based Moody's and Fitch said earlier this month that Ambac faced "moderate" risk of falling below benchmarks for its rating category. Fitch said it was reviewing the guarantors' insurance of collateralized debt obligations backed by subprime mortgages.

CDOs take pools of securities and then slice them into pieces with different credit ratings, from no rating through AAA.

Ambac fell four cents to $23.98 at 9:53 a.m. in New York Stock Exchange Composite trading. The shares had fallen 73 percent this year before yesterday.

Ambac, which pioneered municipal-bond insurance in 1971, has been rated AAA since 1979. When backing debt, the financial guarantors agree to make principal and interest payments if an issuer cannot, allowing the debt to get the highest rankings.