WASHINGTON (By Carl Hulse, NYTimes) March 10, 2006 — After more than five years of allowing President Bush relatively free rein to set their course, Republicans in Congress are suddenly, if selectively, in rebellion, a mutiny all the more surprising since it centers on the party's signature issue of national security.

In a rebuke to the White House, House Republicans are moving aggressively to put the brakes on the takeover by a Dubai company of some port terminal operations in several large American cities, an effort that moved forward on Wednesday with broad bipartisan support.

At the same time, Republicans in the Senate are wrestling with how hard to press the White House for more authority over Mr. Bush's eaves dropping program, seeking a middle ground between Democratic calls for an investigation of the program and White House demands to keep hands off.

In the case of the port deal, the political considerations are clearly paramount for Republicans and are compelling. Public opinion appears to be strongly against allowing an Arab company to manage some port terminals in the United States, Democrats are hammering Republicans on the issue, and the White House has been unable to provide much political cover to its allies on Capitol Hill.

When it comes to the debate over how and whether to allow eaves dropping without warrants on terror suspects, the politics are more muddled. The White House has had considerable success defining that issue on its terms, as antiterrorist surveillance, and there has been no broad public outcry against it. Republicans on Capitol Hill have been left grappling with how to balance their concerns about granting the president wide wartime powers against the perception that they might weaken a program that the administration says protects Americans from attack.

Still, even a limited move to place a check on the eaves dropping program, like the one contained in a deal worked out by the White House with Republicans on the Senate Intelligence Committee on Tuesday, contributes to a sense that Mr. Bush's own party is edging away from him — or, in the case of the port deal, abandoning him and his dismal poll numbers with the greatest possible haste. A perception that conditions in Iraq show little improvement is not helping the relationship.

The president and his Congressional allies have been at cross-purposes before, but it has never reached the level of the port confrontation. The conflict reflects a view held by many Republicans that the White House has asked a lot of them over the years, but has responded with dismissive and occasionally arrogant treatment — a style crystallized in Mr. Bush's quick threat, with little or no consultation, to veto any effort to hold up the port deal legislatively.

Intramural fights in politics often have an element of calculation if not orchestration, and the White House's political shop is no doubt aware that allowing Congressional Republicans to put some distance between themselves and Mr. Bush in an election year could serve the party's long-term interest.

Whether theatrics or something more fundamental, some Republicans say that the port fight and scrutiny of the surveillance program show a new willingness to confront the White House and that it is a fitting moment for Congress to declare its independence.

"If there was ever a good time for Congress to figure out oversight, it would be in the sixth year of a presidency," said Representative Roy Blunt of Missouri, the No. 3 House Republican, well aware that the party in power typically loses seats at the midpoint of a president's second term.

That instinct for political survival is helping to stiffen the Congressional spine. Republicans have held a significant political advantage over Democrats on the issue of national security, offsetting Democratic strength on social policy. Given the uproar at home over the port deal and nervousness about the implications of eaves dropping without warrants, Republicans are worried about losing their edge. Democrats say they should be.

In a memorandum to Senate Democrats that quickly made its way to reporters, a pollster reported Wednesday that the opposition to the port proposal and uncertainty over Iraq have significantly eroded Republican advantages among voters when it comes to security concerns.

"With huge majorities opposing the president's proposal to sell control of U.S. ports to Dubai and the failure of the president's Iraq policy, Republicans' once-yawning advantage on security issues has been largely neutralized," said the pollster, Mark Mellman.

Democrats tried to press their advantage Wednesday in the Senate. Senator Charles E. Schumer of New York surprised Republicans with an amendment to a lobbying bill that would ban any company "wholly owned or controlled by any foreign government that recognized the Taliban" from managing port facilities. The company at issue, DP World of Dubai, fits that description.

Senate Republican leaders, trying to buy the administration some time on the port fight as their counterparts in the House deserted Mr. Bush, blocked a vote. But a showdown appeared inevitable.

"We know what the people of America think," said Senator Richard J. Durbin of Illinois, the No. 2 Democrat in the Senate. "This is a very bad idea."

There was no hesitation on the part of House Republicans, as the Appropriations Committee voted 62 to 2 to bar DP World from taking over any port operations, adding the ban to a $92 billion spending measure for Iraq and Hurricane Katrina recovery that could reach the floor next week.

Speaker J. Dennis Hastert said the House opposition to the deal was less about politics than national security. "We will continue to use our best judgment on how to protect the American people," he told reporters.

While the ruptures over national security have been striking, the administration and Congressional Republicans are likely to be parting ways on other issues waiting in the wings. They include immigration policy, spending cuts, trade and perhaps a stem cell research proposal that many Republicans believe is crucial to winning moderate voters.

The rifts reflect different strains of ideology within the party, many of which have been tamped down until now by Mr. Bush's ability to hold Republicans together, a degree of clout that seems to be ebbing.

Mr. Bush's strength has largely been anchored in his standing on national security. And in elections since the attacks of 2001, that has been good politics as Republicans have claimed the mantle of the party best able to prevent another terror strike.

In the Senate, this week's maneuvering over the surveillance program showed a more cautious approach to confronting the administration. Republicans feared being accused of tampering with an antiterror technique, but some were genuinely troubled by the eaves dropping and refused to reject Democratic calls for an inquiry without taking some action.

The result was a proposal for close oversight by a new subcommittee. But what was most striking was how hard Republicans involved in the negotiations sought to make clear that the agreement was a concession by the White House, not a victory for Mr. Bush.

"They wanted the status quo," said Senator Pat Roberts, Republican of Kansas and chairman of the Intelligence Committee.

One thing is clear: Republicans on Capitol Hill are no longer entrusting security issues solely to Mr. Bush. They now realize that in some cases, they must protect themselves.