WASHINGTON - Merchants triumphed over bankers in a battle for billions Wednesday as the Senate voted to let the Federal Reserve curb the fees that stores pay financial institutions when a customer swipes a debit card. It was murkier, however, whether the nation's consumers were winners or losers.

As a result of the roll call, the Fed will be allowed to issue final rules on July 21 trimming the average 44 cents that banks charge for each debit card transaction. That fee, typically 1 to 2 percent of each purchase, produces $16 billion in annual revenue for banks and credit card companies, the Fed estimates.

The central bank has proposed capping the so-called interchange fee at 12 cents, though the final plan could change slightly.

Victorious merchants said the lowered fees should let them drop prices, banks said they could be forced to boost charges for things like checking accounts to make up for lost earnings and each side challenged the other's claims. Consumer groups were not a united front, either: While the consumer group U.S. PIRG said consumers would benefit, the Consumer Federation of America took no formal stance but said it was concerned about what both industries might do.

Travis B. Plunkett, the consumer federation's legislative director, said the amount of savings that stores pass on to consumers would depend on how competitive their markets are. He said he also worried that the Fed's current proposal might be too restrictive, which might tempt banks to "use that as an excuse to increase charges on customers they value the least, low- to moderate-income customers."

In Wednesday's vote, senators trying to thwart the Fed's rules needed 60 votes to prevail but fell six votes short, 54-45. That delivered a victory for Sen. Richard Durbin, D-Ill., the Senate's No. 2 Democrat, who muscled the provision into last year's financial overhaul law requiring the Fed's action.

Durbin's support on Wednesday represented an erosion from last year, when the Senate included Durbin's provision in the overhaul bill on a 64-33 vote. Much of the drop was explained by a dozen senators - including nine Democrats - who switched from backing Durbin in 2010 to voting to delay the Fed action on Wednesday.

Of the 12, just four are seeking re-election next year: Sens. Kirsten Gillibrand, D-N.Y.; Ben Nelson, D-Neb.; Debbie Stabenow, D-Mich.; and Roger Wicker, R-Miss.

Thirty-five Republicans joined 19 Democrats in backing the unsuccessful effort to block the Fed. Thirty-two Democrats, 12 Republicans and an independent voted to let the central bank move ahead, while Sen. Joseph Lieberman, I-Conn., did not vote.

Wednesday's roll call shot down a proposal by Sens. Jon Tester, D-Mont., and Bob Corker, R-Tenn., that would have delayed the Fed rule for a year. In the meantime, the Fed and three other agencies would have studied whether the Fed's current proposal is fair and rewritten it if at least two agencies decided it wasn't.

Edmund Mierzwinski, consumer program director for US PIRG, which represents state public interest research groups, said some banks might curtail the rewards programs that many attach to their debit cards, such as awarding cash back or airline miles. But he said checking account fees would not rise.

"There will be competition," Mierzwinski said. "Banks will be forced to come up with innovative ways to lower costs in their card networks."

Camden R. Fine, president of the Independent Community Bankers of America, challenged that, saying the Senate vote would mean that "consumers of lower socio-economic status will get hammered" because bank fees would rise.

"Where do people think banks get the money to subsidize these products" like free checking accounts, he said. He also challenged assertions that stores would pass the savings from lower fees to customers.

"Does anybody not smoking dope believe merchants will pass some big windfall to consumers?" he said, adding later, "I mean, what are they going to cut prices by, a penny?"

Merchants, however, argue that they will be forced to lower prices to reflect the curbed debit card fees.

"The retail industry is the most competitive business environment going today," said Brian Dodge, spokesman for the Retail Industry Leaders Association, which represents many large merchants like Target and Home Depot. "There is no doubt competition would drive any interchange savings out of the system, which would be reflected by lower prices."

Affirming that was Dennis Lane, who has owned a 7-Eleven store in Quincy, Mass., for 37 years. He said he pays $7,000 to $10,000 annually in credit card swipe fees.

"Whenever I can reduce my cost of doing business, any responsible retailer reduces costs to the consumer," he said. He also said those savings could allow him to hire summer workers.

On the other hand, the head of a credit union in Mountain Home, Idaho, said slashing debit cards fees would have a huge cost for his business.

Curt Perry, president of Pioneer Federal Credit Union, says cutting the fee to 12 cents per swipe would cost him $780,000 a year. The new fee system would not take into account such expenses as covering fraud, which he said cost him $170,000 last year, leaving him considering options like charging a fees for debit cards or checking accounts.

"We'd have to pass that on, we'd need to generate that revenue from somewhere," he said.