Analysts said investors had expected the U.S. central bank to extend its bond-buying program - dubbed "Operation Twist" - but noted some were disappointed that it stopped short of more aggressive measures to boost growth in the face of slower U.S. hiring and a festering European debt crisis.

In Operation Twist, which was to end this month, the Fed sells short-term debt it holds to buy longer-term bonds in hopes of lowering long-term borrowing costs.

Fed Chairman Ben Bernanke said that policymakers were ready and able to do more if needed, but offered few specifics.

"The most dovish investors were looking for something a little more concrete about the path to more easing, but so far, Bernanke has sounded non-committal," Standard Chartered currency strategist Mike Moran said. "He's leaving the door ajar, but that's still a slight disappointment for some."

John Canally, investment strategist and economist at LPL Financial, said "there were a lot of guys out there with the finger on the 'sell' button unless they saw balance-sheet expansion."

The Dow Jones industrial average dipped 12.94 points, or 0.10 percent, to 12,824.39 at the close. The Standard & Poor's 500 Index edged down 2.29 points, or 0.17 percent, to 1,355.69. But the Nasdaq Composite Index inched up 0.69 of a point, or 0.02 percent, to 2,930.45.

The MSCI index of global stocks edged up 0.2 percent, while the euro rose 0.1 percent to $1.27, helped partly by reports that Greek conservatives had succeeded in forming a coalition government.

Bond prices also swung from gains to losses throughout the day, with the 30-year Treasury bond ending up 8/32 to yield 2.72 percent. But the benchmark 10-year U.S. Treasury note slipped 6/32 to yield 1.65 percent.

U.S. crude oil for July delivery expired at Wednesday's close, settling at $81.75 per barrel - down $2.28, or 2.71 percent for the day.

"Crude futures have been following the stock markets, which have been strong in anticipation of the Fed move," said Mark Anderle, trader for TAC Energy in Dallas. "Now that the Fed's done it, we're going through the 'buy the rumor, sell the news' phase."

SIGNS OF PROGRESS IN EUROPE

Whatever disappointment markets felt after the Fed was tempered by signs that Europe's leaders were making progress on a long-term plan to resolve the continent's debt crisis. That helped push the FTSE Eurofirst 300 index of top European shares up 0.5 percent.

German government bond yields also retreated from record lows after European leaders said they were aiming to hammer out a plan next week to integrate the region's banking sectors.

The United States and other nations have long urged Europe to embrace common banking supervision and deposit insurance to break the cycle of indebted governments having to take on more debt to bail out troubled banks.

A proposal to use the eurozone's new rescue fund to buy sovereign debt and reduce governments' borrowing costs helped ease selling pressure on other European bond markets.

Spain's 10-year government bond yield, a gauge of the compensation investors demand to lend to the government, fell 27 basis points to 6.77 percent. The equivalent Italian yield fell 15 basis points to 5.77 percent.

Spot gold fell $11.26, or 0.70 percent, to $1,606.20. Gold hit its 2012 high around $1,790 in February when the Fed said it would keep interest rates near zero through 2014.