Some of the largest U.S. banks were ranked very low for retail customer satisfaction, a marketing research company said on Thursday.

The study implies that as some of the biggest banks get bigger, customers may not be happy.

Smaller banks and even large regional banks fared better than their colossal counterparts, according to the survey from J.D. Power and Associates.

The three biggest U.S. retail banks — JPMorgan Chase & Co’s Chase, Citigroup’s Citibank, and Bank of America Corp’s Bank of America — consistently rank at or near the bottom for customer service in the regions they serve, the survey said.

Of course the difference between relative levels of customer satisfaction may not be that material — in most regions, the J.D. Power’s customer satisfaction index scores for the top banks were 10 to 15 percent higher than the weakest banks.

But even that small difference can be enough to make customers switch their banks. Only 34 percent of customers surveyed said this year that they “definitely will not” switch banks in the next twelve months, compared with 46 percent in 2007.

Being big can make providing good customer service more difficult, said Michael Beird, director of banking at J.D. Power and Associates.

“It’s spotty and it’s very geographic. US Bancorp, for example, has done well in some regions and not in others. That’s the challenge for the larger banks — how do they create a consistent level of delivery,” he said.

Overall, customer satisfaction in banks in general in 2010 edged lower from last year, with J.D. Power’s index of satisfaction falling to 748 from 749, out of a scale of 1,000.

J.D. Power compiled its 2010 U.S. Retail Banking Satisfaction Study based on the responses of almost 48,000 online respondents. The latest edition of the four-year-old survey was conducted in January and February of this year.