MIAMI (Reuters) - The US government and UBS AG asked a federal judge yesterday to delay the start of a closely-watched trial, as they seek to resolve their dispute over US demands for the identities of thousands of wealthy Americans suspected of using the Swiss bank to dodge taxes.

The request, in a joint court filing, came as the clock ticked down to the trial set for this morning in Miami, where US authorities had been expected to move forcefully to pry the lid off Switzerland's much-vaunted tradition of bank secrecy.

In their filing, the US Justice Department and UBS asked that the trial be postponed until August 3, giving the Swiss and US governments time "to continue their discussions seeking a resolution of this matter".

The Justice Department declined further comment, but UBS and the Swiss government have been signalling for weeks that they were open to an out-of-court settlement of the case.

The case has been widely seen as perhaps the biggest challenge yet to Switzerland's bank secrecy. There was no immediate response from US District Judge Alan Gold, who is presiding over the case and was to have begun hearing arguments Monday about why he should force UBS to disclose information on up to 52,000 wealthy US clients suspected of tax evasion.

But UBS said the motion for a delay would be formally submitted for the court's approval this morning.

In a court order last week, Gold asked the Justice Department to spell out how far it was willing to go to learn the identity of Americans with secret accounts at UBS, the world's biggest wealth manager by assets.

He asked specifically about "receivership and/or seizure of UBS' assets within the US" to enforce the demand that account data be turned over to US tax authorities.

Such remedies might be requested of the court, Gold said, if UBS failed to comply, or was prevented from complying by the Swiss government. He gave the US Justice Department until 1 p.m. yesterday to respond.

Switzerland has vowed to prevent UBS from handing over client information to US authorities, in an attempt to defend bank secrecy, and says the tax case targeting its biggest bank is souring diplomatic ties. In a separate court filing yesterday, the Justice Department said it was still prepared to step up its legal fight against UBS. But apart from unspecified "monetary sanctions" it stopped short of saying what penalties it might seek to impose.

Michael Weinstein, a former trial attorney with the Justice Department in Washington, DC, said yesterday's request for a delay in the case pointed toward likely progress in talks aimed at settling the tax dispute.

"I am of the philosophy that the US won't take the nuclear option to seize the assets of UBS in the US," Weinstein said, citing risks to the economy and also the fact that they may be able to get the names by other, less confrontational means.

The US government was criticised in 2002 over the collapse of accounting firm Arthur Andersen with the loss of thousands of jobs.

Andersen failed to reach a settlement with the Justice Department over its auditing of Enron and surrendered its audit licence after being found guilty on a single criminal charge. The US Supreme Court eventually overturned the verdict but Andersen never recovered.

The UBS case, which comes during a global fight against tax cheats supported by the US administration, has damaged the UBS brand and could result in an expensive settlement for the bank. Swiss media have said UBS may have to pay anywhere from $2.76 billion to $4.6 billion.