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.

The Fed will now issue final rules July 21 that will trim the average 44 cents that banks charge for each debit card transaction. That fee, typically 1 percent to 2 percent of each purchase, produces $16 billion in annual revenue for banks and credit card companies, the Fed estimates.

In Wednesday’s vote, senators trying to keep the Fed from issuing its 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 on swipe fees.

Republican Sens. Olympia Snowe and Susan Collins of Maine, who favored Durbin’s proposal last year to lower the swipe fees, voted Wednesday not to delay the changes.

The Federal Reserve has proposed capping the so-called interchange fee at 12 cents, although the final plan could change slightly.

Victorious merchants said the lowered fees should help them reduce 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: The consumer group U.S. PIRG said consumers would benefit, but the Consumer Federation of America took no formal stance, saying 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.”

Wednesday’s roll-call vote 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 means “consumers of lower socio-economic status will get hammered” because bank fees will rise.

“Where do people think banks get the money to subsidize these products” like free checking accounts, he asked. 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. “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 (that) competition would drive any interchange savings out of the system, which would be reflected by lower prices.”