JACKSON HOLE, Wyo. — The Federal Reserve chairman, Ben Bernanke, delivered a detailed and forceful argument Friday for new steps to stimulate the economy, reinforcing earlier indications that the Fed is on the verge of action.

Calling the persistently high rate of unemployment a “grave concern,” language that several experts described as unusually strong, Bernanke made clear that a recent run of tepid rather than terrible economic data has not altered the Fed’s will to act, because the pace of growth remains too slow to reduce the number of people who lack jobs.

In setting the stage for action when the Fed’s policymaking committee meets in two weeks, Bernanke appeared to defy political pressure from Republicans to refrain from new measures. Mitt Romney, the Republican presidential nominee, has said such action would be counterproductive, and he has pledged to replace Bernanke at the earliest opportunity.