Sonoma County has filed its own lawsuit against LIBOR — the collection of banks caught in an international rate-fixing scandal — alleging it was short-changed on investment returns.

The suit filed Friday in U.S. District Court in San Francisco seeks a return of undetermined losses to local investing agencies including schools, special districts and county government.

It comes on the heels of similar suits from San Mateo County and the University of California claiming damages from financial institutions that set the London Interbank Offered Rate, which is the global benchmark for interest rates.

"It's a question of making sure whatever wrong is made right," said Jonathan Kadlec, Sonoma County's assistant treasurer-tax collector.

Named in the suit are more than 20 current and former LIBOR members including Barclays, Bank of America and Citigroup.

The complaint lists seven causes of action such as fraud, unjust enrichment and violation of antitrust laws.

It focuses on transactions from 2007 to 2010, a period in which Barclays has already admitted its role in manipulating interest rates, said Nanci E. Nishimura, an attorney representing the county in the suit.

"Everybody has been affected by the manipulation," Nishimura said. "We can't afford to take the brunt."

Kadlec, who oversees a countywide investment pool of about $1.5 billion, said an investigation is ongoing to determine the extent of the losses.

He said LIBOR-type investments are a relatively small percentage of the total pool. They involve floating securities in which interest was based on the index, he said.

The lawsuit said the county invested $96 million in those investments in 2007 and $61 million in 2008.

"We never carried a large balance of those types of investments," Kadlec said. "It's a relatively small percentage, even for that time frame."

According to the complaint, the institutions reaped billions of dollars by overstating or understating borrowing costs and artificially setting rates.

The county treasurer's office is responsible for investing funds from the agencies in securities such as treasury notes and bonds issued by corporations and entities like Fannie Mae and Freddie Mac.

Kathleen Larocque, deputy county counsel, said the county joined the lawsuit after consulting first with officials in San Mateo County.

"We talked to them about what the period of time was, looked at what was outstanding and determined it was probably worthwhile to move forward," she said.

The Board of Supervisors discussed it in closed session and reported a decision to go forward a few weeks ago, she said.

Both sides will go before a judge Sept. 25 for a case management conference.

You can reach Staff Writer Paul Payne at 568-5312 or paul.payne@pressdemocrat.com.