“If we continue to settle for weaker standards here, we will continue to pay the price,” wrote Sam Olens, the Republican Georgia attorney general, and George Jepsen, his Democratic counterpart in Connecticut. They urged top prosecutors in other states to sign a separate letter to Visa, MasterCard, JPMorgan Chase, Bank of America and other institutions, pushing them to adopt the chip-and-PIN technology.

Banking groups were swift to issue their own statement, saying that merchants had been “spreading an outdated narrative.” In November, a spokesman for Mr. Olens confirmed that he had taken his name off the letter.

“While the attorney general still supports chip and PIN, we have no further comment at this time,” the spokesman, Nicholas Genesi, wrote in an email.

On Monday, Mr. Jepsen and eight other attorneys general sent the financial institutions a revised version of the letter. While they urged the adoption of chip and PIN “as soon as possible,” the prosecutors made it clear that they were seeking neither a deadline nor a law to make such adoption mandatory.

“We are sensitive to the concern that locking into the law any particular card security technology may pose risks to future innovation and/or give rise to incompatible technical requirements in different jurisdictions,” they wrote.

Banks insist the chips and a signature are enough, and argue that retailers are seeking to deflect attention from the real threat to consumers: weaknesses in retailers’ security systems that have allowed hackers to steal credit card data in a series of breaches. And they point out that by some estimates, only about half of retailers, or even fewer, will be able to process chip-enabled cards by the end of the year.

“We think the focus should be for retailers to turn on their chip readers and use the technology that’s available to them,” said James Chessen, the executive vice president and chief economist at the American Bankers Association, an industry trade group.