(REUTERS) - The Federal Reserve must take immediate action to inject new life into a moribund U.S. recovery, or risk letting the nation settle into a permanently lower growth path, a top Fed official said on Monday.

There is simply too much at stake for us to be excessively complacent while the economy is in such dire shape, Chicago Fed President Charles Evans said in remarks prepared for delivery to the Ball State University Center for Business and Economic Research. It is imperative to undertake action now.

Evans, known for his dovish views on inflation, was the only Fed policy maker to dissent last month on the decision to leave monetary policy unchanged. Then, as today, he called for further easing to boost the recovery.

The U.S. central bank has clearly missed on its mandate to foster maximum employment and is in danger of undershooting its 2 percent inflation goal for the foreseeable future, Evans said.

Without new monetary stimulus, Evans warned, the U.S. could become mired in a 1930s-like Depression, impairing economic growth permanently as the skills of the unemployed atrophy and businesses defer new investment.

To avoid such a scenario, Evans argued, the Fed should promise to keep interest rates near zero as long as unemployment remains somewhat above its natural rate, so long as inflation does not threaten to rise above 3 percent.

While 3-percent inflation may sound shocking, he said, research shows that central banks should fight liquidity traps by allowing inflation to run above target over the medium term.

Since high U.S. unemployment is probably due to the effect of a liquidity trap rather than a structural shift in the economy, Evans said, added monetary stimulus is justified.

And if, he said, it turns out that the real problem was indeed structural and easier policy sparks a rise in inflation, the Fed can simply tighten policy before it threatens to reach the hyperinflationary levels of the 1970s.

We would also know that we had made our best effort, he said.

Unemployment measured at 8.6 percent in November, and most estimates of the natural rate of unemployment hover around 5 percent to 6 percent.

Evans had previously suggested setting the unemployment trigger for monetary policy tightening at 7 percent, but did not mention any specific figure in his prepared remarks on Monday.

The Fed's policy-setting panel meets next week to discuss what, if any, action to take to boost an economy dogged by persistently high unemployment. While many Fed officials appear to be supportive of some change in Fed communications, only a few have said they would support Evans' proposal.

Next week will be the last time Evans votes on the panel until 2013.

(Reporting by Ann Saphir, Editing by Chizu Nomiyama)