Mr. Cecala said that while consumers should not feel the effects of the move in terms of access to credit, the absence of Fannie Mae as a backer could make Bank of America’s mortgage terms and rates less competitive in the future. A spokesman for Fannie Mae declined to comment.

Bank of America revealed the decision in a filing with the Securities and Exchange Commission on Thursday. The direct cause was the dispute over the repurchases, but it comes as Bank of America is reducing its overall size and streamlining its business, and shrinking its mortgage business in particular.

Meanwhile, Fannie and Freddie face questions over what role they will play in the housing market, as policy makers in Washington prepare to overhaul the government’s relationship with the mortgage industry.

Bank of America ranked as the nation’s second-largest originator of home loans for all of 2011, with an 11.6 percent market share, but by the fourth quarter it had slipped into fourth place behind Wells Fargo, JPMorgan Chase and Citigroup, according to Inside Mortgage Finance. Wells, in particular, has been an aggressive competitor, picking up much of the slack in the market and now accounting for one out of every four mortgage originations.

Bank of America, once the nation’s largest bank by assets, has been steadily shrinking its balance sheet, and now ranks second to JPMorgan Chase. Many of its problems stem from the disastrous 2008 decision to buy Countrywide Financial, a subprime mortgage lender that caused Bank of America to record more than $30 billion in losses.

Investors are concerned that Fannie and Freddie, along with private investors, will force Bank of America and other giant mortgage lenders to repurchase tens of billions in mortgages that later defaulted, arguing they were not made with adequate documentation or proof of income, or otherwise failed to conform to proper underwriting standards.

Bank of America and its competitors have argued that many homeowners defaulted because of unemployment, the weak economy and other factors, not errors in the origination process.

Still, repurchase fears weighed on Bank of America shares in particular last year, and at one point Bank of America’s stock fell below $5 a share. Its shares closed at $8.02 on Thursday, up 7 cents.