Lawsuits are mounting against some of the world’s biggest banks over the ma­nipu­la­tion of the global interest rate known as Libor as smaller lenders, municipalities and investors take stock of losses tied to the widening scandal.

The cases are believed to be a trickle before an oncoming deluge of civil litigation that will beset the world’s largest banks for years. Yet the ultimate problem for the accused may not be the millions they pay in damages but rather the cloud of uncertainty looming over their business.

Already there is talk of the government stepping in to oversee a global settlement, just as it did in the mortgage robo-signing scandal. But it took years for regulators to reach a nationwide mortgage settlement. And that settlement involved the cooperation only of states, not countries, which means the banking industry could be mired in legal action for a while.

Dozens of lawsuits have been filed in the wake of a $450 million settlement U.S. and British regulators reached last month with the London-based bank Barclays, which admitted manipulating Libor rates for profit and to hide the bank’s financial distress from 2005 to 2009. Libor, or the London interbank offered rate, is an average of bank interest rates that underpins trillions of dollars’ worth of worldwide financial transactions.

In one of the latest Libor cases, Berkshire Bank is suing all 16 banks involved in setting the rate, claiming loss of income. The New York-based institution, with $881 million in assets, claims in a class-action lawsuit that rate-fixing lowered the interest payments it received from August 2007 to May 2010. “Tens, if not hundreds, of billions of dollars of loans are originated or sold within this state each year with rates tied to Libor,” Berkshire said in a complaint filed Wednesday. Keeping the rate artificially low “on the date on which a loan resets will generally reduce the amount of interest that a lender receives by an equivalent amount.”

Berkshire hopes to represent several hundred banks and credit unions that are based in New York or have a majority of their operations in the state. The case could serve as the model for countless lenders as Libor is the benchmark for the financial products known as derivatives.

“There will be a waterfall of derivative lawsuits,” said Karen Shaw Petrou, managing partner of Federal Financial Analytics, a Washington research firm. “Each will be different because the alleged harm by plaintiffs is different — different investments, different time periods, different outcomes.”

Given the universe of securities dependant on the rate, financial experts say money managers such as Vanguard Group or BlackRock may enter the legal fray on behalf of their clients.

Investment firm Charles Schwab laid the groundwork last year with a lawsuit against 11 Libor-setting banks that allegedly depressed returns on mutual funds and short-term debt by rigging the rate. Around the same time, municipalities including Baltimore City accused the banks of robbing them of millions in returns on financial instruments used to fund public infrastructure.

Regulators are investigating potential Libor-related fraud at other big banks on the panel, meaning additional settlements are probably in the works. Researchers at Keefe Bruyette & Woods estimate the banks involved will have to cough up between $30 billion and $50 billion to settle all of the fines, penalties and civil cases.

“It’s a manageable expense considering the size of these banks,” said analyst Frederick Cannon at Keefe Bruyette & Woods. “But this is going to give a big impetus to a lot of the regulations concerning capital markets activities generally — a stronger Volcker rule, moving all derivatives to exchanges.”

It is too soon to gauge the regulatory impact of the Libor investigations. Regulators on both sides of the Atlantic are debating alternatives to Libor, but there are no definitive plans to change the rules governing the rate. Long-term regulatory implications are difficult to pin down, much like the full scope of the civil lawsuits. Members of Congress have raised concerns about whether banks would need taxpayer assistance to compensate victims of the Libor scheme. U.S. Federal Reserve Chairman Ben S. Bernanke, speaking before the Senate banking committee, said that if the central bank “can contribute to a global settlement as we did in the case of the [mortgage] servicers, we would, of course.”

Federal Financial Analytics’ Shaw Petrou said a global settlement would be difficult to achieve given the number of agencies and entities involved. Moreover, such a settlement would do little to stem the wave of civil suits.

A number of the class-action suits hinge on the claim that banks violated antitrust laws by conspiring to fiddle with the rate. E-mails between traders released by Barclays could be used as evidence of a price-fixing conspiracy.

Lawyer Richard Holwell of Holwell Shuster & Goldberg said breach of antitrust laws, namely the Sherman Act, will probably serve as the basis for a majority of suits filed in the coming months.

“The hurdles in proving damages are a lot lower under the antitrust analysis than they are under a securities fraud analysis,” said Holwell, a former judge in the Southern District of New York.

Berkshire Bank is taking a different approach by alleging the banks violated New York state’s common law of fraud. Plantiffs, in that instance, would have to prove the banks intentionally rigged the rate.

Columbia University law professor John Coffee anticipates there will be a few large class-action suits but expects more individual civil cases brought by mutual funds and investment banks.

“Mutual funds economize on their operating costs and would love to settle rather than litigate for four or five years,” he said. “If one of these cases was litigated on a full-scale basis, the plaintiff might have to incur costs of well over $10 million to bring the case to trial.”