WASHINGTON — Lender CIT Group has filed for Chapter 11 bankruptcy protection in an effort to restructure its debt while trying to keep loans flowing to thousands of midsize and small businesses.

CIT made the filing in New York bankruptcy court Sunday, after a debt-exchange offer to bondholders failed. CIT said in a statement that its bondholders have overwhelmingly approved a prepackaged reorganization plan that will reduce total debt by $10 billion while allowing the company to continue to do business.

“The decision to proceed with our plan of reorganization will allow CIT to continue to provide funding to our small-business and middle-market customers, two sectors that remain vitally important to the U.S. economy,” said Jeffrey M. Peek, chairman and CEO. Peek has said he plans to step down at the end of the year.

CIT’s move will wipe out current holders of its common and preferred stock, likely meaning the U.S. government will lose the $2.3 billion it sank into CIT last year to prop up the ailing company. The government could have lost billions more, however, had it not declined to hand over more aid to the company earlier this year.

The Chapter 11 filing is one of the biggest in U.S. corporate history. CIT’s bankruptcy filing shows $71 billion in finance and leasing assets against total debt of $64.9 billion. Its collapse is the latest in a string of huge cases driven by the financial crisis over the past two years, as bailed-out industry heavyweights such as General Motors and Chrysler entered bankruptcy court.

CIT has been trying to fend off disaster for several months and narrowly avoided collapse in July. It has struggled to find funding as sources it previously relied on, such as short-term debt, evaporated during the credit crisis.

It received $4.5 billion in credit from its own lenders and bondholders last week, reportedly made a deal with Goldman Sachs to lower debt payments and negotiated a $1 billion line of credit from billionaire investor and bondholder Carl Icahn. But the company failed to persuade bondholders to support a debt-exchange offer, a step that would have trimmed at least $5.7 billion from its debt burden and given CIT more time to pay off what it owes.

It is unclear what the filing will mean for the nation’s small businesses, many of which look to CIT for loans to cover expenses such as buying materials at a time when other credit is hard to come by.

Analysts have warned that already ailing sectors, such as retailers, could be hit especially hard because CIT serves as the short-term financier for about 2,000 vendors that supply merchandise to more than 300,000 stores.