GENEVA (AP) - Swiss lawmakers failed to resolve a split yesterday on whether to allow a referendum on a treaty with the United States that will hand Washington thousands of files on suspected tax cheats.

Parliament's upper and lower house will now have to hammer out a compromise today.

On Tuesday, lawmakers in Switzerland's lower house accepted the deal that will see the country's biggest bank, UBS AG, divulge the names of 4,450 American clients suspected of tax evasion to US authorities. But the lower house also voted to allow the Swiss public to approve the deal in a referendum before it becomes law - a move the upper house has repeatedly rejected.

Agreement between the two houses is necessary for the final approval of the deal, which the government hopes will eventually end UBS's three-year battle with US tax authorities that culminated in revelations the bank had for years helped American clients hide millions of dollars in offshore accounts.

The Internal Revenue Service has said the US tax agency expects Switzerland to honor the agreement to divulge the names by August - a deadline the Swiss would likely miss if a referendum is called.