NEW YORK >> Americans prefer using their debit cards at the register. But a small fee could change that.

A new Associated Press-GfK poll finds that about two-thirds of consumers use debit cards more frequently than credit cards. But when debit card holders were asked how they would react if they were charged a $3 monthly fee for their debit card, 61 percent say they’d find another way to pay.

If the fee was $5, 66 percent would do the same. If the fee was $7, the figure rises to 81 percent.

The findings come at a time when consumers are seeing unwelcome changes to their debit cards and the checking accounts to which they’re linked. Although banks haven’t started imposing monthly fees for debit cards, there are signs higher costs could be on the way.

Starting in October, a new cap will sharply limit the revenue banks can collect from merchants whenever customers swipe their debit cards. That revenue has been a critical income source for banks; merchants paid issuers $19.7 billion for debit transactions in 2009, according to the Nilson Report, which tracks the payments industry.

Consumers are already seeing the fallout. Chase, PNC Bank and Wells Fargo ended or scaled back their debit rewards programs, citing the new regulation. The availability of free checking accounts also declined last year for the first time since 2003.

And more changes could be in store.

Chase, for example, is testing a $3 monthly fee for debit cards on new accounts in northern Wisconsin. In Atlanta it’s testing a $15 monthly fee on basic checking accounts.

Among the AP-GfK poll respondents who say they would leave their debit cards in their wallets in the face of such fees, more say they’d pay with cash, 53 percent, or check, 42 percent, rather than another form of plastic.

Debit card fees would cause 22 percent to switch to credit cards, and 12 percent say they would switch to a prepaid spending card.

For now the notable preference for debit could be linked to a negative sentiment about credit cards; nearly half of respondents to the AP-GfK poll say the interest rates they are charged are unfair.

That might be because 30 percent had their interest rates hiked in the past two years. That’s more than twice the number who say their rates were lowered.

Forty-two percent of respondents also say the fees and penalties on their cards are unfair; 37 percent say card issuers recently raised those potential charges.