WASHINGTON - President Bush has quietly claimed sweeping new powers to open Americans' mail without a judge's warrant, the Daily News has learned.

The President asserted his new authority when he signed a postal reform bill into law on Dec. 20. Bush then issued a "signing statement" that declared his right to open people's mail under emergency conditions.

That claim is contrary to existing law and contradicted the bill he had just signed, say experts who have reviewed it.

Bush's move came during the winter congressional recess and a year after his secret domestic electronic eavesdropping program was first revealed. It caught Capitol Hill by surprise.

"Despite the President's statement that he may be able to circumvent a basic privacy protection, the new postal law continues to prohibit the government from snooping into people's mail without a warrant," said Rep. Henry Waxman (D-Calif.), the incoming House Government Reform Committee chairman, who co-sponsored the bill.

Experts said the new powers could be easily abused and used to vacuum up large amounts of mail.