"We have roughly $135 billion left of uncommitted resources. The rest is out the door," he said on ABC Television's "This Week with George Stephanopoulos."
Geithner said that figure included "a very conservative judgment about how much money is likely to come back from banks that are strong enough not to need this capital now to get through a recession."
Congress approved $700 billion last fall for rescuing banks that had gotten into trouble when the U.S. housing boom crashed, but lawmakers and ordinary Americans show signs of becoming increasingly unhappy over the program.
Geithner wouldn't specify whether he expects to ask Congress for more money this year, though he didn't rule it out. "The important thing is we are going to work with the Congress to make sure we have the resources needed to do this right," he said.
"We have substantial resources, we're going to use them quickly, as carefully as we can...to get credit flowing again and we'll cross that bridge when we come to it in terms of whether we'll need additional resources," Geithner added.
He conceded that banks likely will need "large amounts of assistance" before the credit crisis is resolved and said it would be "a mistake" to think that they can earn their way out of the current downturn.
"To get through this, governments need to act. There's a great obligation and responsibility for government to act to solve these things," Geithner said. "The market will not solve this and the great risk for us is that we do too little, not that we do too much."
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