When the Federal Reserve talked about keeping interest rates low until mid-2014, Wall Street heard it as a promise.

If you read the Fed's statement from two weeks ago, however, it was little more from a forecast, and it came from a central bank whose forecasts have sometimes been wrong. Following a stronger-than-expected jobs report last week, some economists are already questioning the wisdom of trying to pin down rates more than two years in the future.

Paul Kasriel, chief economist at Northern Trust in Chicago, says he believes the first increase in short-term interest rates will come in 2013, a full year earlier than the Fed's statement indicates. He points to six straight months of growth in bank credit, which leaves businesses and consumers with more money to spend.

That means we should see continued job growth and, by sometime next year, inflation moving above the Fed's 2 percent target.

The central bank would then face a tough choice: Either tolerate more inflation or move interest rates higher. Since it has just been told that rates will stay low until 2014, the market may take the latter as a nasty surprise.

"I think it was an ill-advised exercise," Kasriel says of the statement mentioning 2014. "I think it's only a forecast, and they should make that very clear."

Some people inside the Fed agree with him. James Bullard, president of the St. Louis Federal Reserve Bank, has criticized the two-year-plus rate forecast. In a speech this week, he said that "a near-zero rate policy stretching over many years can begin to distort fundamental decision-making in the economy in ways that may be destructive to longer-run economic growth."

One concern, Bullard said, is that low rates punish savers. These tend to be older people, who end up with less income to spend. Bank savings accounts now pay less than 1 percent, which means savers are losing ground to inflation, and a 10-year Treasury note yields just over 2 percent.

Stretch out the extremely low rates for more than five years - the Fed first set its benchmark rate at zero in December 2008 - and that effect is magnified. What initially felt like a temporary drop in income begins to seem permanent.

The Fed also has tied its own hands by putting more specific language in its statements. For a long time, it talked about keeping rates low for an "extended period," a vague phrase that was generally understood to mean at least one year. Then, last August, the central bank said the "extended period" would last until mid-2013.

Now, it has tacked on another year. Stephen Williamson, a professor of economics at Washington University, says he's not surprised that markets interpreted mid-2014 as something more than a forecast.

"They don't like going against their own commitments," Williamson said of the Fed. "It's quite bad if they tell you they are going to do something and then don't do it. This is critical for their credibility."

If Kasriel is right, our central bank will face a major credibility test sometime next year. If it is forced to raise rates earlier than expected, markets would lose confidence in the Fed's forecasting ability. Future pronouncements would be taken with a grain of salt, and the Fed's policies would become less effective.

The Fed has performed admirably in guiding the economy out of a very deep hole. It may have overreached, though, by exaggerating its ability to predict the distant future.