Hopes and fears for the struggling United States economy are focused on the country's central bank, set to announce what it intends to do help spark a recovery.

The U.S. Federal Reserve concludes its two-day meeting later Wednesday, with many economists predicting the bank's policy board will move to further lower borrowing rates in order to spur growth. But leading Republican lawmakers have taken the unusual step of writing a letter to the Fed, urging the central bank to do nothing.

The letter, signed by House Speaker John Boehner and Senate Minority Leader Mitch McConnell, warned the central bank to “resist further extraordinary intervention,” saying such moves had yet to help boost the economy. They also warned new action could do “further harm.”

A leading Democratic senator, Charles Schumer, criticized the letter, accusing Republicans of meddling in the central bank's affairs.

Federal Reserve Chairman Ben Bernanke has repeatedly said the central bank still has ways to help spark economic growth. But the Fed's board of governors has been divided over what action to take, if any.

The U.S. Federal Reserve is set up as an independent decision-making entity. Fed Chairman Ben Bernanke is a Republican and was first appointed by Republican President George W. Bush. He was then renominated by Democratic President Barack Obama.

Many economists say the Fed is likely to announce a policy known as “Operation Twist,” in which it substitutes short-term securities in its $1.7 trillion portfolio for longer-term holdings. The goal of such a move would be to lower yields on U.S. Treasury bonds in the hopes of driving down consumer borrowing rates.

The Fed's benchmark lending rate is already at an all-time low of zero to one-quarter of a percent.

The U.S. unemployment rate is at 9.1 percent.