WASHINGTON — Janet L. Yellen, the Federal Reserve chairwoman, delivered an upbeat message on the state of the American economy to Congress on Wednesday, highlighting the strength of job growth and indicating that the Fed remained on course to begin reducing its bond holdings in the fall.

Ms. Yellen added, however, that the Fed was paying close attention to the recent weakness of inflation. While emphasizing that she expected prices to start rising more quickly, she said persistent weakness could lead the Fed to raise interest rates more slowly.

“It’s premature to reach the judgment that we’re not on the path to 2 percent inflation over the next couple of years,” she said. “We’re watching this very closely and stand ready to adjust our policy if it appears the inflation undershoot will be persistent.”

Ms. Yellen’s testimony before the House Financial Services Committee lifted stock prices and lowered bond yields on Wednesday. Investors tend to celebrate any sign that the Fed might slow the pace of its interest-rate increases.