NEW YORK (Bloomberg) — Ambac Financial Group Inc., the bond insurer facing a crippling credit-rating downgrade, may get $3 billion in new capital as part of a rescue agreement with banks, according to a person with knowledge of the discussions.

An announcement may come early next week, said the person, who declined to be named because no details have been set. The New York-based company rose 16 percent in New York Stock Exchange trading on Friday after CNBC Television said Ambac and its banks were preparing a deal.

A rescue that enabled Ambac to retain its AAA rating for the municipal and asset-backed securities guarantees would help banks and municipal debt investors avoid losses on securities it insures. Banks stood to lose as much as $70 billion if the top-rated bond insurers, which include MBIA Inc. and FGIC Corp., lose their credit ratings, Oppenheimer & Co. analysts estimated.

"It's been on the table for a while and if it happens it will certainly be a good thing for any bond insurer that gets a capital infusion," said Donald Light, a senior analyst covering insurance at Celent, a consulting firm in Boston. Ambac spokeswoman Vandana Sharma declined to comment specifically on the discussions.