Bradley C. Bower/Bloomberg

Wells Fargo on Tuesday settled accusations that it sold troubled mortgage investments without fully researching the products or disclosing the risks to customers.

The action by federal authorities, the latest mortgage-crisis case against a big bank, yielded a $6.5 million settlement. Wells Fargo earned $16 billion last year.

The Securities and Exchange Commission has spent nearly four years building cases against the nation’s biggest banks for their role in the mortgage mess. The agency has filed civil actions against Goldman Sachs, JPMorgan Chase and Citigroup.

But in recent months, the agency has struggled to bring big cases as it pursued a second round of investigations focused on the banks’ failure to disclose the dangers of mortgage securities. The Wells Fargo case comes just days after Goldman Sachs revealed that the S.E.C. had closed an investigation into a 2006 mortgage deal without pursuing charges.

In an order against Wells Fargo and one of its former brokers, the Securities and Exchange Commission charged that the bank had failed to study or even understand the complexity of the high-risk investments it sold. In the period leading up to the bursting of the housing bubble, the S.E.C. said, Wells Fargo sold so-called asset-backed commercial paper to nonprofit groups, local governments and other investors with “generally conservative investment objectives.”

“Broker-dealers must do their homework before recommending complex investments to their customers,” Elaine C. Greenberg, head of the agency’s Municipal Securities and Public Pensions Unit, said in a statement. The $6.5 million penalty, the S.E.C. said, will go into a fund for aggrieved investors.

As part of the settlement, Wells Fargo is neither admitting nor denying the charges. A bank spokeswoman said “these issues occurred more than five years ago and pertain to a part of the firm that was completely revamped after the merger with Wachovia,” a bank it bought at the end of 2008. She added that Wells Fargo was “pleased to put this matter behind us.”

The Wells Fargo case involved investments sold from January to August 2007, as the subprime mortgage crisis was brewing. Several investors, according to the S.E.C., “suffered substantial losses” after three of the deals defaulted later that year.

“Municipalities and other nonprofit institutions were harmed because Wells Fargo abdicated its fundamental responsibility as a broker to have a reasonable basis for its investment recommendations to customers,” Ms. Greenberg said.

The S.E.C. criticized the bank for not informing investors about the “the nature and volatility of the underlying assets.” The lack of transparency stemmed, in part, from the bank’s own ignorance, the agency said.

Wells Fargo and its brokers, the S.E.C. said in the statement, “failed to understand the true nature, risks and volatility” of the deals it pushed on investors. Rather than reviewing memos outlining the risks, the bank relied almost entirely on the credit ratings of the securities.

The action also cited Shawn McMurtry, a former vice president and broker at the bank, over his role in selling the deals. Under the settlement, Mr. McMurtry agreed to a $25,000 fine and six-month suspension from the securities industry.