WASHINGTON — Janet L. Yellen, the Federal Reserve chairwoman, said on Wednesday that the country’s economic expansion had broadened and strengthened, and that she expected the growth to continue.

Ms. Yellen’s upbeat assessment, delivered to the Joint Economic Committee, is likely to reinforce expectations the Fed will raise its benchmark interest rate in mid-December. It could also sharpen questions about Republican plans for a major tax cut aimed at stimulating faster growth.

“Economic growth appears to have stepped up from its subdued pace early in the year,” she told the Congressional committee. “Moreover, the economic expansion is increasingly broad, based across sectors as well as across much of the global economy.”

The hearing may have been Ms. Yellen’s last appearance before Congress in her current role. Her four-year term as the Fed chairwoman ends in early February, and she has said that she plans to leave as soon as her successor is sworn in. President Trump has nominated Jerome H. Powell, a Fed governor since 2012, to serve as the its next chairman.