WASHINGTON — A signing statement attached to postal legislation by President Bush last month may have opened the way for the government to open mail without a warrant. The White House denies any change in policy.

The law requires government agents to get warrants to open first-class letters. But when he signed the postal reform act, Bush added a statement saying that his administration would construe that provision “in a manner consistent, to the maximum extent permissible, with the need to conduct searches in exigent circumstances.”

“The signing statement raises serious questions whether he is authorizing opening of mail contrary to the Constitution and to laws enacted by Congress,” said Ann Beeson, an attorney with the American Civil Liberties Union. “What is the purpose of the signing statement if it isn’t that?”

Beeson said the group is planning to file a request for information on how this exception will be used and to ask whether it has already been used to open mail.

White House Press Secretary Tony Snow said there was nothing new in the signing statement.

In his daily briefing Snow said: “All this is saying is that there are provisions at law for — in exigent circumstances — for such inspections. It has been thus. This is not a change in law, this is not new.”

Postal Vice President Tom Day added: “As has been the long-standing practice, first-class mail is protected from unreasonable search and seizure when in postal custody. Nothing in the Postal Accountability and Enhancement Act changes this protection. The president is not exerting any new authority.”

Sen. Susan Collins, R-Maine, who guided the measure through the Senate, called on Bush to clarify his intent.

The bill, Collins said, “does nothing to alter the protections of privacy and civil liberties provided by the Constitution and other federal laws.”

“The Foreign Intelligence Surveillance Act of 1978 and our federal criminal rules require prior judicial approval before domestic sealed mail can be searched,” she said.

Sen. Charles E. Schumer, D-N.Y., criticized Bush’s action.

“Every American wants foolproof protection against terrorism. But history has shown it can and should be done within the confines of the Constitution. This last-minute, irregular and unauthorized reinterpretation of a duly passed law is the exact type of maneuver that voters so resoundingly rejected in November,” Schumer said.

The ACLU’s Beeson noted that there has been an exception allowing postal inspectors to open items they believe might contain a bomb.

“His signing statement uses language that’s broader than that exception,” she said, and noted that Bush used the phrase “exigent circumstances.”

“The question is what does that mean and why has he suddenly put this in writing if this isn’t a change in policy,” she said.

In addition to suspecting a bomb or getting a warrant, postal officials are allowed by law to open letters that can’t be delivered as addressed — but only to determine if they can find a correct address or a return address.

Bush has issued at least 750 signing statements during his presidency, more than all other presidents combined, according to the American Bar Association.

Typically, presidents have used signing statements for such purposes as instructing executive agencies how to carry out new laws.

Bush’s statements often reserve the right to revise, interpret or disregard laws on national security and constitutional grounds.

“That non-veto hamstrings Congress because Congress cannot respond to a signing statement,” ABA President Michael Greco has said. The practice, he has added, “is harming the separation of powers.”

The president’s action was first reported by the New York Daily News.

The full signing statement said:

“The executive branch shall construe subsection 404(c) of title 39, as enacted by subsection 1010(e) of the act, which provides for opening of an item of a class of mail otherwise sealed against inspection, in a manner consistent, to the maximum extent permissible, with the need to conduct searches in exigent circumstances, such as to protect human life and safety against hazardous materials, and the need for physical searches specifically authorized by law for foreign intelligence collection.