Financial institutions in the United States probably need hundreds of billions of dollars in additional assistance, and one congressman wants to harness state and local pension funds to help them.

Rather than rely more heavily on the Treasury, which has already put $350 billion in the nation’s banks, Representative Gary L. Ackerman sees an opportunity in the trillions of dollars in public pension funds. Most of the funds suffered giant losses last year in the market turmoil. But they do not need all of their assets immediately, because their time horizon for paying benefits is decades long.

Mr. Ackerman, Democrat of New York, is sponsoring legislation that would allow public pension funds to pool some of their money and use it to create a sole-purpose entity that would buy $50 billion to $250 billion worth of preferred stock in America’s banks. That would strengthen the banks’ balance sheets and, Mr. Ackerman hopes, get them lending again.

“Some of us are getting tired of writing checks with public money” and seeing no results, Mr. Ackerman said. He said pension fund officials who had heard about the measure so far were eager to participate.