But she said that it was up to Congress and the White House to evaluate the details of proposed changes.

“Looking at the likely impact of the particular proposals that may be under consideration is something that we haven’t done carefully at the Federal Reserve,” she said.

Ms. Yellen also said that the Fed would evaluate changes in fiscal policy in deciding how quickly to raise interest rates. The Fed could seek to dampen the effects of tax cuts by raising rates more quickly.

Fed officials have drawn a careful distinction between changes that increase economic capacity, for example by encouraging business investment, and changes that provide a short-term sugar high, for example cuts in personal income taxes that are likely to increase spending.

The Fed estimates that the economy is already growing at something close to the maximum sustainable pace, so a short-term boost might simply drive up inflation.

“We welcome strong growth,” Ms. Yellen told Congress. “The Fed is not trying to stifle growth. We’re worried about trends that could push inflation above our 2 percent objective.”

Asked about the idea of a trigger as part of tax legislation, Ms. Yellen said that she shared concerns about the growth of the federal debt. “When you look at for example CBO’s long-term budget projections, it’s the type of thing that should keep people awake at night,” she said, referring to the Congressional Budget Office’s projections that federal debt will grow by $10 trillion over the next decade.