Switzerland has agreed to hand over details of about 4,450 UBS AG bank accounts to U.S. authorities to settle a tax dispute that challenged Swiss banking secrecy and now threatens to spill over to other banks.

With Switzerland's famed banking secrecy under fire, the Swiss have also agreed to process requests by the United States seeking information from its banks besides UBS about account holders who may have tried to evade U.S. taxes.

This announcement today should send a signal - no matter what institution you're with, the IRS is willing to pursue both the institution and the individual, Internal Revenue Service Commissioner Doug Shulman told reporters on Wednesday.

The accounts were at one time worth $18 billion, Shulman said, though he could not provide a current figure.

U.S. authorities would not name any other foreign banks under probe but the IRS is expected to use the Swiss deal as a template to pursue further prosecutions.

The IRS is now gaining institutional skill and knowledge in how to pursue these types of cases and they're going to use that. This is, I believe, the beginning and not the end, said Peter Hardy, a former federal prosecutor and specialist in white-collar crime at Post & Schell in Philadelphia.

The UBS dispute had strained relations between the United States and Switzerland and challenged the latter's jealously guarded bank secrecy laws. The deal may add steam to a global effort among cash-strapped governments to crack down on tax-evading jurisdictions.

But the settlement could help UBS, the world's second-largest wealth manager, restore an image that has been battered by the financial crisis and the U.S. dispute, and may open the way for the Swiss government to sell its UBS stake.

It's good to get this out of the way but the confidence of a lot of clients has been compromised so I'm not sure we will see inflows return in Q3. It will take time to recover reputation from this, said Jaap Meijer, an analyst at Evolution Securities in London.

Switzerland's Finance Minister Hans-Rudolf Merz said the government wants to sell its stake as quickly as possible and while it would be good business, it also has to consider other factors.

UBS shares closed down nearly one percent at 16.74 Swiss francs, having reversed some of their earlier losses. Swiss rival Credit Suisse ended down 1.3 percent and Julius Baer dropped 0.8 percent.

UBS Chairman Kaspar Villiger said the agreement helps resolve one of UBS' most pressing issues. I am confident that the agreement will allow the bank to continue moving forward to rebuild its reputation through solid performance and client service.

In February, UBS agreed to pay $780 million and disclose about 250 client names to settle a criminal probe by U.S. authorities. One former UBS banker testified that he smuggled a client's diamonds into the United States in a tube of toothpaste.

Wednesday's deal effectively ends a separate civil lawsuit by U.S. authorities that sought up to 52,000 account names.

OTHER BANKS

Other Swiss banks are fretting that the U.S. taxman's spotlight may now fall on them. The Wall Street Journal reported on Wednesday that more European banks have been identified in the U.S. tax probe, including Switzerland's Credit Suisse, Julius Baer, Zuercher Kantonalbank and Union Banque Privee (UBP).

Switzerland may claim its banking secrecy remains intact, but some private bankers say it is no longer a selling point for its banks, which will need to offer other skills like wealth management and legacy planning to attract clients.

The majority of assets in Swiss private banks are from European Union citizens, said David Williams, an analyst at Fox-Pitt Kelton in London. I think it won't be long before we see action from the European Union along similar lines.

The new treaty between the United States and Switzerland would allow action in the case of tax fraud and the like in the UBS case, the Swiss government said. Precise details will be published 90 days after the agreement comes into force.

The U.S. government retains the right to go back and use a summons to collect the names, which roughly equal the number of accounts, if the settlement process fails, said IRS chief Shulman.

The client accounts to be disclosed will likely belong to people suspected of committing tax fraud under the terms of a double taxation agreement that obliges Switzerland to provide help if Washington seeks it in a criminal investigation.

Shulman said notices from UBS to clients would go out in stages, but warned U.S. citizens to come forward now.

Once the Swiss government turns over names, all bets are off, Shulman said, noting these clients could face civil and criminal prosecution.

Under a temporary amnesty program in effect until September 23, U.S. citizens can come forward and declare accounts, pay fines and in general avoid criminal prosecutions.

The UBS case has added significant steam to that program. The agency saw about 400 people come forward during one week in July compared to about 100 during all of 2008 alone.

(Additional reporting by Steve Slater in London and Jeremy Pelofsky in Washington; Editing by Erica Billingham and Tim Dobbyn)

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