U.S. Federal Reserve Board Chair Janet L. Yellen testifies before the Senate Banking, Housing and Urban Affairs Committee on Tuesday. (Win McNamee/Getty Images)

Federal Reserve Board Chair Janet L. Yellen expressed hope Tuesday morning that the slowdown in the U.S. job market would prove temporary, but she emphasized that the central bank would be cautious in raising interest rates again.

Yellen, testifying before the Senate Banking, Housing and Urban Affairs Committee, acknowledged that hiring has dropped off sharply in recent months, but she also pointed to early signs that wages are beginning to rise after years of stagnation. She said she is "optimistic" that the progress in employment will continue.

"We believe that will turn around, expect it to turn around, but we are taking a cautious approach … to make sure that expectation is borne out," Yellen told lawmakers.

The Fed is responsible for charting the course for the nation’s economy, with the dual mission to keep prices stable and strengthen employment. It does that by adjusting the influential federal funds rate. A higher rate helps curb inflation by making borrowing money more expensive, which discourages spending and investment and reins in economic growth. A lower rate means that money is cheap, stimulating purchases by households and businesses. That helps boost employment and speeds up the economy.

The Fed chief's assessment comes less than a week after the Fed unanimously voted to leave its benchmark interest rate unchanged. The central bank raised rates in December for the first time since the Great Recession but has not done so again amid persistent concerns about the health of the global economy.

Yellen said Tuesday that there is still "considerable uncertainty" over her outlook, with such risks as slow growth at home, turbulence in China and volatility in financial markets.

The most immediate threat comes from across the Atlantic Ocean, where Britain will vote Thursday on whether to remain in the European Union. A decision to exit — popularly known as Brexit — would upend Britain's four-decade partnership with the continent and throw the future of Europe’s open market into doubt.

Already, the British pound has been on a roller coaster as the probability of departure shifts with each poll. International policymakers have warned that a decision to leave would lower economic growth in the country by more than 5 percent over the next three years and potentially ripple across the rest of the world.

"A U.K. vote to exit the European Union could have significant economic repercussions," Yellen said Tuesday.

In the aftermath of the 2008 financial crisis, the Fed slashed its target rate all the way to zero and pumped trillions of dollars into the economy in a bid to bolster the American recovery. More than seven years later, it is finally in the process of withdrawing that support.

The first move was in December, when the Fed nudged its target rate up to a range of 0.25 to 0.5 percent. At the time, officials anticipated raising rates four times this year, but the uncertainty in the global economy has forced them to downgrade that projection. Most Fed officials now think only two rate hikes are warranted this year, and a growing number think only one will be necessary.

That shift in thinking at the central bank is evident in Yellen’s own statements. Just last month, she had signaled that the central bank could raise rates "probably in the coming months." But Yellen dropped the reference in a speech early this month, after disappointing government data showed employers added just 38,000 jobs in May. And last week, she told reporters that she is "not comfortable to say it's in the next meeting or two."

On Tuesday, Yellen made the case for caution. Because rates are already so low, the Fed has limited room to reduce them further if the economy were to weaken, she said. Moving gradually also gives the central bank time to assess whether its forecast of continued economic improvement will come true.

"Our cautious approach to adjusting monetary policy remains appropriate," she said.

The Fed has faced criticism from both the left and the right recently over its governance. Sen. Richard C. Shelby (R-Ala.), chairman of the Banking Committee, opened the hearing Tuesday by calling on the Fed to follow more stringent rules for setting policy and to explain when it deviates.

"The desire to preserve the Fed’s independence, however, should not preclude consideration of additional measures to increase the transparency of the board’s actions," he said.

Meanwhile, Sen. Sherrod Brown (D-Ohio) focused on diversity within the Fed’s top ranks. Last month, more than 100 lawmakers sent a letter to Yellen arguing for more minority representation among its leadership.

The central bank is led by a board of governors based in Washington and 12 regional bank presidents scattered throughout the country. The governors are appointed by the president and confirmed by the Senate, but regional bank leaders are chosen by local boards of directors.

Those officials tend to be white men. Yellen is the first woman to serve as chair in the central bank’s 101-year history. Only three Fed governors have been African American, and there have been no black regional bank presidents. No one now in the top brass is Hispanic.

In addition, an analysis by the progressive Center for Popular Democracy found that 83 percent of the boards of directors are white and 75 percent are male. The group also found that 39 percent of directors come from the financial industry, while 11 percent are from community groups, labor organizations or academia.

Yellen said the central bank is committed to increasing diversity throughout the organization.

"I do believe we are making some progress, but I want us to make greater progress," she said.

Yellen will testify Wednesday before the House Financial Services Committee.

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