A group of 11 jurors will decide whether Wells Fargo & Co. grossly mismanaged a former securities lending program and lied about its safety, or whether the financial calamity that followed the boom was to blame for millions of dollars in losses.

Lawyers painted vastly different pictures of the multibillion-dollar program in opening statements Tuesday in federal court in St. Paul before U.S. District Judge Donovan Frank. The San Francisco-based bank marketed the program to institutional investors such as pension funds.

The investors accuse Wells Fargo of fraud in playing fast and loose with what was supposed to be a very conservative investment program. They assert that the bank failed to properly monitor and manage the collateral investments, then lied to participants about the performance while investments melted down.

Of the total securities in the portfolio in the fall of 2007, nearly 15 percent were distressed or had defaulted.

The investors say that instead of investing funds in safe investments such as high-grade money market instruments, as they were led to believe, managers were making riskier bets on complicated instruments such as structured investment vehicles, or SIVs.

One such SIV, Cheyne Finance, was run by a London hedge fund and invested in subprime mortgages. Cheyne was put into a receivership.

“Mr. Stumpf runs the bank,” Minneapolis lawyer Michael Ciresi said, referring to Wells Fargo CEO John Stumpf. “He didn’t even know what an SIV was. He had to go to Wikipedia.”

Wells Fargo has denied the allegations. It sold the majority of its ClearLend securities lending business to Citigroup Inc. in 2011 and has largely exited the securities lending business.

In court Tuesday, a lawyer for Wells Fargo characterized the program’s investments as “reasonable, safe and conservative” at the time. The unit had a good track record, he said, until the financial crisis — and even then the losses were a small percentage of the overall program.

“Nothing Wells Fargo did or did not do harmed investors,” said Bart Williams, a Los Angeles lawyer for Wells Fargo.

“The Wells Fargo securities lending program, and the people who ran it, performed at an extraordinarily high level at times of the most unthinkable stress,” Williams said. “We will prove that Wells Fargo’s primary interest at all times was the welfare and best interest of all the members and participants in the securities lending program.”

Investors were clearly warned in writing that they could suffer some losses, he said.

The case is one of at least four ongoing lawsuits in Minnesota over the bank’s former multibillion-dollar securities lending program, and the second jury trial in Minnesota over the program.

Wells Fargo lost an identical case in 2010 after a six-week jury trial in Ramsey County District Court. In that case, also brought by Ciresi, jurors determined the bank breached its fiduciary duty and engaged in fraud. They awarded nearly $30 million in damages to four charitable foundations, with an additional award of damages and attorneys’ fees and interest bringing the total to about $57 million.

Wells Fargo appealed, but the verdict was upheld.

One of the other lawsuits over the program that Wells Fargo is facing in Minnesota, filed by the City of Farmington Hills Employee Retirement System in 2010, is set for trial Sept. 16. Judge Frank certified that lawsuit as a class action last year.

Wells Fargo’s securities lending program involved the securities, mostly stock, that the institutional investors kept in custodial accounts at the bank. They authorized Wells Fargo to lend the securities to borrowers, typically third-party brokers who used the shares for their own trading.

In exchange, the brokers paid Wells Fargo cash collateral that Wells Fargo would invest until the loaned securities were returned to the bank’s clients and the cash collateral was returned to the brokers.

The lawsuit focuses on the cash collateral investments Wells Fargo made largely from 2005 to 2008.

The trial that opened Tuesday involves a lawsuit filed against Wells Fargo in 2011 by a group of about 13 institutional investors, including Blue Cross and Blue Shield of Minnesota, the North Memorial Health Care Pension Plan and the St. John’s University Endowment.

The trial, however, specifically covers the claims by just six of the plaintiffs in the lawsuit — those that are not covered by the Employees Retirement Income Security Act (ERISA). Judge Frank will hear the claims of plaintiffs covered by ERISA separately.

Altogether, the six plaintiffs in the jury trial suffered $8.2 million in losses. If they are successful, lawyers will seek punitive damages, too.

Plaintiffs in the jury trial include CentraCare Health System, on behalf of itself and the Sisters of the Order of Saint Benedict Retirement Plan; the Jerome Foundation, a nonprofit arts group in St. Paul; Nebraska Methodist Health System, the North Memorial Health Care Pension Plan; the Order of Saint Benedict, as the St. John’s University Endowment and the St. John’s Abbey Endowment; and the El Paso County Retirement Plan in Colorado.

Oddly, three Wells Fargo entities, including the bank itself, the Wells Fargo Foundation and a fixed-income fund that’s related to the bank, are members of that class and did not opt out of the lawsuit. “Wells Fargo is suing Wells Fargo,” Ciresi said.

The other plaintiffs include the Blue Cross Blue Shield of Minnesota Pension Equity Plan; pension plans at Meijer Inc.; the International Truck and Engine Corp. Retiree Supplemental Benefit Trust; the Twin City Hospitals-Minnesota Nurses Association Pension Plan; the Twin Cities Hospital Pension Plan for Licensed Practical Nurses, and the Chicago Area Joint Welfare Committee for the Pointing, Cleaning and Caulking Industry Local 52.