Peter Schneider/Keystone, via Associated Press

The Swiss government said on Wednesday that it would allow its banks to disclose information on American clients with hidden accounts, a watershed move intended to help resolve a long-running dispute with the United States over tax evasion.

The decision, which comes amid widening scrutiny in Europe of tax havens, is a turning point in what has been an escalating conflict between Switzerland and the United States.

Eveline Widmer-Schlumpf, Switzerland’s finance minister, said the move would enable Swiss banks to accept an offer by the United States government to hand over broad client details and pay fines in exchange for a promise by United States authorities not to indict any banks.

Disclosure of actual client names and account data, which American authorities have been aggressively seeking, would take place under a taxation treaty between the two countries that the American side has not yet ratified. Banks under criminal scrutiny that agree to cooperate with the decision could still face deferred-prosecution or nonprosecution agreements, a lesser punishment than indictment.

Ms. Widmer-Schlumpf declined to say how much banks might have to pay. But she said the Swiss government would not make any payments as part of the agreement. Sources briefed on the matter say the total fines could eventually total $7 billion to $10 billion, and that to ease any financial pressure on the banks, the Swiss government might advance the sums and then seek reimbursement.

“It is important for us to be able to let the past be the past,” Ms. Widmer-Schlumpf said at a news briefing in Bern, Switzerland. She declined to give any details about the program, but said banks would have one year to decide whether to accept the American offer.

American clients whose names are handed over by Swiss banks but who have not voluntarily disclosed hidden accounts to the Internal Revenue Service would probably face criminal tax-evasion charges, lawyers said. Dozens of Americans have been indicted or charged in recent years for failing to disclose their accounts.

Until now, the Swiss government has been resisting cooperation because the secrecy of its banking system has long made the country an offshore money haven for wealthy foreigners.

The country is also under growing pressure from the European Union to assist in ferreting out citizens who have sheltered money using offshore private banking services. Switzerland is not a member of the European Union, but nations including France and Germany have tired of watching their citizens squirrel away cash with impunity right across their borders.

The European Union is pushing member nations like Luxembourg and Austria to update their own secrecy rules, meaning the Swiss could soon be without an ally in the bloc and be left vulnerable to pressure from other nations.

Ms. Widmer-Schlumpf said the government would work with Parliament to quickly pass a new law that would allow Swiss banks to accept the terms of the United States offer, but said the onus would be on individual banks to decide whether to participate.

“If banks were not authorized to cooperate with the U.S. authorities, the initiation of further criminal investigations or charges concerning banking institutions could not be ruled out,” a Swiss government statement said. It added that “the uncertainty for the financial center would continue to exist.”

In 2012, the United States Justice Department indicted Wegelin & Company, Switzerland’s oldest bank. The bank pleaded guilty in January, putting it out of business, and prosecutors have indicated in recent months that more indictments could be coming.

Calling the decision “a good, a pragmatic solution for the banks to emerge from their past,” Ms. Widmer-Schlumpf said, “We expect this to create the base for banks to again gain some room for maneuver so that calm can return to the sector.”

There is no certainty that Parliament would pass the law after two of Switzerland’s biggest parties, the Social Democrats and the People’s Party, voiced their opposition and a third, the Christian Democratic People’s Party, said it disagreed with the urgency the new law was put forward.

Igor Moser, a spokesman for Zürcher Kantonalbank, one of about a dozen Swiss and Swiss-style banks under criminal scrutiny by United States prosecutors, said that if the Swiss Parliament approved the government’s decision, the bank “will be able to agree on an individual solution with the U.S. authorities.” He added that “a possible penalty will be part of this individual agreement.”

Ms. Widmer-Schlumpf hinted that the repercussions for banks that actively helped clients evade taxes after 2009 would be bigger than for those that stopped such activities that year. “All banks knew after 2009 that they can no longer do all sorts of businesses,” she said.

It was in 2009 that UBS, the largest Swiss bank, agreed to enter into a deferred-prosecution agreement with the United States. The bank eventually turned over 4,450 client names and paid a $780 million fine after admitting criminal wrongdoing in selling tax-evasion services to wealthy Americans. Justice Department authorities were incensed that after the UBS deal, other Swiss banks took in American clients fleeing UBS to provide shelters for their income, according to court documents in cases of some indicted American clients.

Also in 2009, Switzerland and the United States signed a protocol amending a 1996 tax treaty governing exchanges of information on Americans suspected of avoiding taxes. While the protocol has been approved by the Swiss Parliament, it has been held up in the United States Senate, blocked by Senator Rand Paul, a Republican from Kentucky. The protocol makes it easier for American authorities to seek client and account data from Switzerland.

The Swiss decision on Wednesday to turn over any American client names appears to be contingent on the American side passing the protocol. The decision said any names release would “occur exclusively within the scope of administrative assistance procedures based on a valid double taxation agreement.”

In the meantime, Swiss banks would be free to disclose to American authorities broader statistical data about American clients, like information about business relationships. Such disclosure would then pave the way for banks under criminal investigation to negotiate settlements with United States authorities.

“This is an important step for the banks; it will apparently allow them to disclose statistical information, such as the number of accounts with U.S. beneficial owners, the number of accounts with foreign corporations or foundations, and the amount of assets under management,” said Scott Michel, a tax lawyer in Washington, D.C. “The I.R.S. and D.O.J. can use this information as the basis for financial penalties under settlement agreements, which might be deferred-prosecution agreements or nonprosecution agreements.”

The decision also requires Swiss banks that cooperate with the Justice Department to protect their bankers and employees from, among other things, being fired for cooperating. American authorities have indicted more than two dozen Swiss bankers, lawyers and financial advisers in recent years.

Other Swiss banks that have been the targets of United States inquiries include Credit Suisse, which disclosed in July 2011 that it had received a letter saying it was under a grand jury investigation; the Zurich-based Julius Baer; two cantonal, or regional, banks; the Swiss operations of HSBC Holdings; and three Israeli banks, Bank Hapoalim, Mizrahi-Tefahot Bank and Bank Leumi.

Resolution of the conflict “has taken longer than it should have, with a lot of otherwise avoidable damage suffered on the Swiss side,” said Robert Katzberg, a white-collar criminal defense lawyer in New York with Swiss and American bank clients. “But it now appears the end is in sight.”

David Jolly contributed reporting.