The country’s biggest banks have made moves to bolster their balance sheets by about $56 billion since the government disclosed the results of its financial “stress tests” two weeks ago, Treasury Secretary Timothy F. Geithner said Wednesday.

Testifying before the Senate Banking Committee, Mr. Geithner said that the financial system had begun to “heal,” and that the Treasury would soon be introducing the next phase of its financial rescue effort  the plan to team up with private investors to buy billions of dollars in toxic assets from banks.

“There are important indications that our financial system is starting to heal,” Mr. Geithner told lawmakers, though he cautioned that it was still too early to talk about an “exit strategy” for the government.