Four Republican senators sought Thursday to legalize use of the National Security Agency to spy on American citizens.

One of the bill's chief sponsors, Sen. Mike DeWine of Ohio, said the bill requires the president to go to court as soon as possible to get approval for wiretapping and other forms of monitoring.

"It does not ... give the president a blank check," DeWine said, while authorizing "a limited, but necessary, program."

The proposal came under immediate criticism from advocacy groups such as the American Civil Liberties Union.

The ACLU said in a statement that the bill would allow "Americans' phone calls and e-mails to be monitored for 45 days without any court oversight and makes court review after that period optional" _ in violation of the Fourth Amendment's guarantees against unreasonable searches.

"Congress cannot approve an illegal program when so many questions remain unanswered," said Caroline Fredrickson, director of the ACLU's Washington legislative office. "When the rule of law has been broken by anyone, especially a president, the proper response is a full and independent investigation."

The bill would give the government up to 45 days to monitor calls and e-mails of suspected terrorists when one party is in the U.S. and the other is overseas. Like Bush's existing program, the government would not have to get court approval.

After 45 days, federal officials would have to stop the eavesdropping, get a court warrant or explain to House and Senate intelligence subcommittees why the monitoring must continue.

Joining DeWine in sponsoring the legislation are Sens. Olympia Snowe of Maine, Lindsey Graham of South Carolina and Chuck Hagel of Nebraska. The senators have working closely with the White House, which has said it generally supports their approach.

Since shortly after the attacks of Sept. 11, 2001, the National Security Agency has monitored the international communications of people inside the United States when their calls and e-mails are believed to be linked to al-Qaida.

The government normally has to get a court order to monitor domestic communications, but Bush signed an executive order directing the NSA to conduct the operations without a judge's approval.