* Parties seek trial delay, saying talks should continue

* Formal ruling on delay expected Monday

* Case seen as biggest challenge yet to Swiss bank secrecy

* Thousands of suspected US tax dodgers may be identified (Adds additional Justice Department comment)

By Tom Brown

MIAMI, July 12 (Reuters) - The U.S. government and UBS AG asked a federal judge on Sunday to delay the start of a closely-watched trial, as they seek to resolve their dispute over U.S. 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 9 a.m. EDT 1300 GMT) Monday in Miami, where U.S. authorities had been expected to move forcefully to pry the lid off Switzerland's much-vaunted tradition of bank secrecy.

In their filing, the U.S. Justice Department and UBS (UBSN.VX: Quote, Profile, Research) (UBS.N: Quote, Profile, Research) asked that the trial be postponed until Aug. 3, giving the Swiss and U.S. 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 signaling for weeks that they were open to an out-of-court settlement of the case.