Washington ? Senate Republicans blocked a proposed investigation of President Bush’s domestic spying operation Thursday as the chairman of the Senate Intelligence Committee said he had reached an agreement with the White House to pursue legislation establishing clearer rules for the controversial program.

But Senate aides described the discussions with the White House as very preliminary. Angry Democrats expressed skepticism about the negotiations, with some describing it as a ploy to protect the Bush administration and the highly classified surveillance operation from congressional scrutiny.

The political maneuvering underscored the stakes surrounding a secret intelligence-gathering program that the White House describes as critical to preventing future terrorist attacks in the United States, but which critics see as unconstitutional and an abuse of executive power.

After a closed-door meeting with committee members, Sen. Pat Roberts, R-Kan., said the panel had “decided to adjourn” without considering a Democratic proposal to launch an investigation of the program, which is run by the National Security Agency, an intelligence agency that operates eavesdropping posts around the globe.

Instead, Roberts, the panel chairman, said the vote was put off because the White House had “committed to legislation and has agreed to brief more Intelligence Committee members on the nature of the surveillance program.”

White House officials confirmed a new willingness to consider legislative fixes after weeks of insisting that no congressional action was necessary.

“We maintain that the president does not need additional congressional authority,” said White House spokeswoman Dana Perino. But she said the administration is now willing to discuss a GOP proposal that contains “some good legislative concepts that would not undermine the president’s ability to protect Americans.”

Meanwhile on Thursday, the Justice Department was ordered by a federal judge to respond within 20 days to requests by a civil liberties group for documents about the NSA program. The Electronic Privacy Information Center had sued the department under the Freedom of Information Act seeking the release of the documents.