U.S. seeks leniency for UBS informant Birkenfeld

MIAMI (Reuters) - U.S. authorities requested a sharply reduced prison sentence on Tuesday for a key informant in their tax evasion prosecutions of wealthy American clients of Swiss bank UBS.

The reduction was requested in a filing with a federal court in Fort Lauderdale, Florida, where former UBS executive Bradley Birkenfeld was due to be sentenced on Friday.

The request was made a day before U.S. and Swiss authorities were due to announce final details of a wider negotiated settlement of their legal dispute over access to the names of American clients of UBS suspected of tax evasion.

In the court filing, prosecutors said Birkenfeld, a U.S. citizen, had faced up to five years imprisonment after pleading guilty in June 2008, to helping a U.S. billionaire hide $200 million in assets from U.S. tax authorities.

The prosecutors asked that Birkenfeld's sentence be cut to 2-1/2 years imprisonment, citing his cooperation in efforts to uncover what they called a "multibillion-dollar scheme to defraud the United States" and evade taxes perpetrated by wealthy American clients of UBS.

UBS and its rich American customers became the target of U.S. probes in 2007 when Birkenfeld first began cooperating with U.S. authorities and helped them start building criminal and civil complaints against the bank.

His evidence, among other breakthroughs in the case, led to the indictment in February 2008 of Raoul Weil, a Swiss citizen who was then head of UBS's wealth management business.

Weil, who has since left UBS and denies any wrongdoing, was charged with conspiring to help thousands of Americans hide $20 billion in assets from U.S. tax authorities.

Weil is currently living in Switzerland, according to his U.S.-based lawyer, and is considered a fugitive from U.S. justice..

(Reporting by Tom Brown; Editing by Pascal Fletcher and Maureen Bavdek)