The Federal Deposit Insurance Corp. estimates that 28 million people in the United States do not have an account at an insured financial institution and 44.7 million are not fully served by the bank relationships they do have.

That means to cash checks, pay bills or borrow money, about 40 million households rely on check-cashing centers, money-wiring operations and payday-loan outlets, where fees and interest rates can be high.

Americans spend at least $10.9 billion on more than 324 million alternative financial transactions a year, the Center for Financial Services Innovation has found.

Now the agency is working with representatives from banks, the government, nonprofit agencies and consumer advocates to brainstorm about how to bring a population it calls the "unbanked" into the financial mainstream.

"It is a critical obstacle to opportunity in this country," FDIC Vice Chairman Martin J. Gruenberg said. "We're having parallel economic systems developing in the United States."

To change that, the FDIC has formed a national initiative called the Alliance for Economic Inclusion, bringing together financial and community organizations in nine markets across the country to find ways to serve the unbanked population.

The FDIC chose Wilmington, Del., as one of the nine target markets because of its high concentration of low- and moderate-income families, a high number of alternative financial centers — the FDIC found 28 of the 91 check-cashing centers in Delaware are in Wilmington — and its strong connection to the banking industry.

"Wilmington was just a good fit," Gruenberg said. "We thought it was a natural location and we're very excited about it."

Other areas chosen as target markets: parts of Alabama; Worcester, Mass.; Chicago; Austin, Texas; Kansas City, Mo.; the Gulf Coast; Baltimore, and Los Angeles.

"We're looking long term," said Bill R. Sorg, vice president of personal financial services at Wilmington Trust. "We're realizing these are the people who are living in our communities and going to our schools. To not serve this market is not a smart thing to do."

But convincing the unbanked to change won't be easy, said Wilmington City Councilman Norman D. Griffiths, who is also chairman of the Metropolitan Urban League.

"They have a distrust of financial institutions," Griffiths told the bankers. "If you're going to compete for this business, you have to understand that."

And despite $1.1 trillion in annual income that the underbanked earn every year, banks have struggled to find a way to build relationships with them. Because banks are highly regulated, every transaction requires paperwork, which adds to the bank's costs.

"From the bank's perspective, you want to make money and reduce risk," said Steven Butler, an Avondale, Pa.-based banking consultant. "With the unbanked, you're talking about small amounts of money and a high number of transactions. How do you make those relationships profitable and as risk-free as possible?"

Daniel A. Weiss, senior vice president of Microfinance International Corp., puts it more bluntly:

"People don't trust banks, but banks don't trust people, also. It goes both directions."

Weiss' Washington, D.C.-based company is trying to fill the gap between traditional institutions and high-fee money lenders by offering micro-loans as small as $500 to people, mostly immigrants, who have no credit history but have shown in other ways that they are credit-worthy.