* Rahn & Bodmer informed of U.S. investigation last week
* Bank says stopped accepting undeclared assets in 2008
ZURICH, Sept 11 (Reuters) - Private bank Rahn & Bodmer is under investigation by U.S. authorities, it said on Wednesday, following a recent deal to allow some Swiss banks to pay fines instead of facing prosecution for tax evasion by their U.S. customers.
That deal applies to about 100 second-tier Swiss banks, which may have to disclose information and face penalties of up to 50 percent of assets they manage for wealthy Americans.
A group of banks already under U.S. criminal investigation includes Credit Suisse, Julius Baer and state-backed regional bank Zuercher Kantonalbank. A second group of dozens more Swiss banks, which also helped weathy Americans hide their assets, are not yet under formal investigation.
"We knew we would have to go to U.S. authorities, so we began to prepare the documentation concerning our U.S. business some months ago, believing we would be in the second group," said Rahn & Bodmer partner Christian Rahn.
"It is difficult to evaluate whether being in the first group of banks is better for us or not," he said.
The bank was informed last week that it was under investigation, Rahn said. A spokeswoman for the U.S. Justice Department declined to comment.
The bank will not need to set aside capital to meet regulatory requirements if it has to pay a fine, as it has provisions which will cover a potential payment, Rahn said.
Credit Suisse and Julius Baer said in July they were preparing information on client withdrawals demanded by U.S. investigators to help pinpoint tax evasion, which may have pointing the finger at other banks.
However, Rahn said he did not believe his bank was being investigated as a result of data passed on by other banks as it had stopped accepting undeclared U.S. assets in 2008 and advised clients with such assets to make voluntary disclosures to the U.S. authorities.
According to its website, the Zurich-based bank managed client assets of 12.5 billion Swiss francs ($13.4 billion) at the end of 2012. It employs about 200 people.
It is the oldest bank remaining in the German-speaking part of Switzerland after St. Gallen-based Wegelin shut its doors earlier this year following an indictment and fine by U.S. authorities for conspiring to help U.S. clients evade taxes.
UBS paid a fine of $780 million in 2009 and delivered the names of more than 4,000 clients to avoid indictment, giving the U.S. authorities the information that has enabled them to pursue other Swiss banks.