New York ? Citibank, the nation’s largest credit-card issuer, has agreed to block online gambling using its credit cards, the state attorney general said Friday.

The agreement announced by the bank and Atty. Gen. Eliot Spitzer is expected to significantly reduce illegal, underage and potentially addictive Internet gambling. It applies to all Internet gambling transactions, not just those in New York, and goes into effect in 60 days.

“Americans now waste $4 billion a year on this pernicious form of gambling,” Spitzer said. “With this agreement, we will cut off an enormous line of credit that was a jackpot for illegal offshore casinos.”