WASHINGTON — As a member of the Senate Judiciary Committee, Sen. Sheldon Whitehouse has condemned the Bush administration in the harshest terms because, in his view, it has damaged civil liberties in the name of counterterrorism.

But Whitehouse is now considering backing President Bush on an overhaul of the nation’s intelligence rules that critics say would undercut the constitutional ban on unreasonable searches. Partly because his seat on the Intelligence Committee has shown him the value of warrantless wiretaps on suspected terrorists, Whitehouse says, he has already joined bipartisan majorities behind Mr. Bush on key surveillance questions.

“The more we know about what terrorists are saying to one another overseas, the better positioned we are to anticipate and defend against what they’re planning,” said Whitehouse, echoing the president’s argument that the law “will help our intelligence professionals learn our enemies’ plans for new attacks.”

One leading opponent of the pending surveillance bill, Sen. Russell Feingold, Democrat of Wisconsin, said it would “profoundly undermine the rule of law.” The liberal Democracy for America said, “This so-called compromise lets AT&T, Verizon and the entire Bush administration off the hook for lying to Americans and illegally tapping our phone calls.”

While Whitehouse said he may yet vote against final passage of the Foreign Intelligence Surveillance Act when the Senate resumes debate after its Fourth of July recess, he played down Feingold’s concerns about the most controversial part of the bill and backed the president in an important test vote that cleared the path for its approval.

The Rhode Island Democrat personifies the dilemma that many of his partisans have faced repeatedly since the Sept. 11 attacks. The demands of protecting the nation against its enemies has presented conflicts with constitutional freedoms that have not proved easy to resolve.

Whitehouse based his 2006 Senate campaign heavily on attacking Mr. Bush. As a junior senator he has attracted attention with his prosecutorial approach to the legal basis for some of Mr. Bush’s most aggressive counterterrorism efforts — including a secret program of warrantless electronic eavesdropping, undertaken to detect the contacts of foreign terrorists inside the U.S.

As the Senate debated the surveillance bill last week, Whitehouse continued his biting criticism of a Bush administration that, in his words, had declared “open season” on certain wiretap targets, without proper constitutional safeguards.

But when push comes to shove, Whitehouse said the objectionable elements of the FISA bill may be outweighed by its value to counterterrorism, plus some provisions to tighten judicial supervision of the spying measures. Whitehouse had an unusual role in the drafting of the pending surveillance bill because of his positions on the two committees that share jurisdiction over the legislation.

One of the main objections raised to the administration’s telephone and e-mail surveillance program has been that it operated outside a system of secret courts created in the original FISA bill of 1978 to guard against spying abuses of that era.

After the program came to light, civil liberties groups sued the telecommunications companies that had assisted the administration in tapping into telephone and e-mail traffic. Meanwhile, the Congress and the White House have struggled for more than a year over the most extensive retooling of the surveillance law in its history.

The first draft of the new FISA bill cleared the Senate Intelligence Committee last summer with a big bipartisan majority that included Whitehouse. That measure acceded to Mr. Bush’s demand that the phone companies get retroactive immunity from any legal liability over their work on the warrantless wiretap program.

Civil libertarians objected strongly, arguing that trying the suits against the companies would bring out evidence of abuses of the spying system and hold the administration accountable. Whitehouse said he, too, was opposed to dismissal of the lawsuits against the phone companies. He explained, however, that he voted for the initial version of the FISA bill because he knew the Judiciary Committee would have a chance to amend it.

In the Judiciary Committee, Whitehouse devoted much effort to safeguards for Americans overseas who might get caught up in U.S. government eavesdropping on e-mail and telephone traffic among suspected foreign terrorists — even if the American citizens were not themselves the targets of wiretaps.

Whitehouse also supported efforts to strengthen and spell out the power of the secret FISA court to monitor foreign surveillance and prevent abuses.

The final version of the intelligence overhaul, negotiated among House and Senate leaders, included elements of the Intelligence and Judiciary Committee drafts, such as a clause spelling out that all the eavesdropping programs had to operate under the jurisdiction of the FISA court. Senate Intelligence Committee Chairman John D. Rockefeller IV said that would prevent any recurrence of the excesses that he attributed to the Bush administration. Critics charged, however, that Mr. Bush had flouted such a provision in the old law because it contained no accountability or sanctions.

The final deal also gave Mr. Bush most of what he wanted to protect the telecommunications firms from lawsuits over their role in his surveillance program. He argued that without such protection it would be difficult to get future cooperation from the telecoms in assisting in counterterrorist surveillance.

Feingold and his allies argued that this provision amounted to what he called a “get out of jail free card” for the phone companies that would close off a path to disclosure of — and accountability for — the Bush administration’s actions in the warrantless wiretap program.

Whitehouse said last week that he will vote for Feingold’s amendment to strip the immunity language from the bill. “It’s a mistake for Congress to be taking ongoing litigation and stepping into the middle of it and declaring who the winners and losers are going to be,” he said.

But he said he might vote for the final bill even if the Feingold amendment and other efforts to beef up constitutional safeguards in the bill do not pass.

“I’m not sure I’m as confident as Russ Feingold is that this litigation will actually end up successfully digging into the conclusion that he thinks it can get to,” he said.

Immunity for the phone companies “isn’t really the only issue,” Whitehouse said. “This is a large and comprehensive bill that solves a whole variety of other problems including ones that I worked very hard to solve.”

The administration, which has long asserted that its surveillance activities have been lawful, now appears to have the votes needed for final passage of the surveillance overhaul.

Enactment of the bill would be “an historic achievement to modernize FISA to reflect dramatic changes in communications technology over the last 30 years,” Attorney General Micahel B. Mukasey and National Intelligence Director J. Michael McConnell said in letter to Senate leaders last week.

If he votes for the bill, Whitehouse will be in good company. It has already passed the House with broad bipartisan support, and it has the support of another strong critic of the administraton’s wiretap program, Illinois Sen. Barack Obama, the Democratic presidential candidate.