WASHINGTON — The Federal Reserve said on Wednesday that it was likely to raise interest rates at the end of 2014, but not until then, adding another 18 months to the expected duration of its most basic and longest-running response to the financial crisis.

The announcement means that the Fed does not expect the economy to complete its recovery from the 2008 crisis over the next three years. By holding short-term rates near zero beyond mid-2013, its previous estimate, the Fed hopes to hasten that process somewhat by reducing the cost of borrowing.