Emboldened by the decline in President Bush's approval ratings, the Iraq prisoner abuse scandal and setbacks in the Iraq war, the Republican Congress is showing signs of taking a more assertive approach to its dealings with the administration.

One Senate committee is holding hearings into abuse of prisoners in Iraq and a second is about to issue a report on intelligence failures before the Iraq war. Early this month, a House Appropriations subcommittee, meeting behind closed doors, quickly rejected Bush's request for a free hand in spending a $25 billion contingency fund for the war in Iraq, stipulating instead how all but $1 billion would be used.

The same day, the Senate voted 95 to 0 to approve the war money with slightly less stringent conditions.

Republican legislators openly -- but seldom for the record -- vent their frustration to reporters about the Bush administration's secrecy, reluctance to consult and seeming contempt for the institution's processes. There have been some instances of rebellion.

Defying a White House veto threat, House and Senate leaders are moving ahead with a six-year transportation bill whose final price tag may be at least $28 billion higher than the figure the administration says is acceptable. Negotiations between GOP leaders in Congress and the White House quickly broke down.

Former House speaker Newt Gingrich (R-Ga.) said the restiveness is real and probably inevitable. "As a practical matter it can't take full form until after the election, but I would be very surprised if by January -- even with Bush reelected -- that you don't see substantially more assertion of oversight."

"The institutional jealousies built into the Constitution do work over time, and they should," he said. "If [the war on terrorism] is going to be a long conflict with an irreconcilable wing of Islam, then I think Congress has to exercise routine oversight and do it routinely."

Former Senate majority leader Robert J. Dole (R-Kan.) said: "I see signs of this, and it's reassuring. When a catastrophic event happens, everyone is going to do almost anything [to help the president]. But when you get down the road a little bit, you want to see what we did wrong or how much money we spent."

Democrats say such scattered actions do not constitute a sea change. "The [GOP-controlled] House has refused again and again to exercise its responsibility for oversight over this administration," says Rep. Henry A. Waxman (Calif.), ranking Democrat on the Government Reform Committee.

Republican leaders, Waxman charged, have rebuffed Democratic requests for investigations of intelligence failures before the Iraq war, the Pentagon's handling of civilian contractors in Iraq, such as Halliburton Co., and the role played by White House officials in leaks leading to the exposure of CIA officer Valerie Plame in a newspaper column.

During a recent House debate on the 2005 defense authorization bill, Republicans blocked a move by Waxman to set up a panel to investigate Abu Ghraib prison abuse in Iraq.

But there have been indications that the Bush administration's long honeymoon with Congress, which was extended when lawmakers in both parties rallied around the president in the aftermath of the Sept. 11, 2001, attacks, may be nearing an end.

Congressional assertiveness has ebbed and flowed in recent decades, often in step with the fortunes of presidents.

It was not until November 1973, when President Richard M. Nixon was reeling from Watergate-related disclosures and U.S. involvement in Vietnam was ending, that Congress reasserted prerogatives given up during the Vietnam War. It passed a joint resolution known as the War Powers Act, requiring regular consultation with Congress on contemplated military action, written notification within 48 hours of such action and other steps.

Democratic gains in the congressional elections of 1974, after Nixon's resignation, swept reformers into power and began a period of activism that produced investigations of the intelligence community, payoffs to foreign governments by international oil companies and other targets.

In 1982, Republicans who controlled the Senate played a pivotal role in seeking to limit the Reagan administration's covert operations against the communist government in Nicaragua, activities that had not been disclosed to Congress. The administration's subsequent attempts to skirt those provisions by diverting private funds to the anti-communist forces blew up into the Iran-contra scandal.

In Waxman's view, the passivity of the GOP-controlled Congress contrasts dramatically with its aggressiveness during the Clinton administration. "There wasn't anything too small for them to have hearings, issue subpoenas and make wild accusations," he said. "In this administration, there isn't a scandal big enough for them to even ask questions."

Congress, however, has recently showed renewed assertiveness in the area where its constitutional prerogatives are most clear: in controlling the purse strings.

Within days of the Sept. 11 attacks, Congress passed emergency legislation giving Bush a free hand to spend $10 billion to aid victims and bolster national defense.

Congress subsequently approved at least $185 billion to fight the wars in Afghanistan and Iraq, often giving the administration unprecedented flexibility to move billions of dollars from several special funds without the usual prior approval from Congress.

But beneath the facade of wartime support for the president, lawmakers in both parties chafed at the lack of accountability, and refused to give the White House the free hand it sought in the use of tens of billions of additional dollars.

Less than two months after the 2001 attacks, House Appropriations Committee Chairman C.W. Bill Young (R-Fla.) complained in writing to the White House that the administration was not complying with statutory requirements to report on the use of funds.

Rep. John P. Murtha (Pa.), a strong pro-defense Democrat, said recently that the Pentagon may have observed the letter of the law but still "abused the trust of Congress."

In 2002, GOP lawmakers learned that the Pentagon was diverting millions of dollars of operating funds to build a network of military facilities in the Persian Gulf region without advising Congress.

The upshot was an unusual provision written into a 2003 spending bill with the support of Republicans and Democrats in Congress. It limited the amount the Pentagon could divert to the construction projects to $150 million a year.

"Funds for these projects have been expended without providing notice to Congress despite repeated requests for information by both House and Senate Appropriations Committees and House and Senate Armed Services Committees, and as required by law," an accompanying report said.

In the latest rebuff to the White House, the defense subcommittee of the House Appropriations Committee earlier this month rejected an administration request for an open-ended allocation of $25 billion for the war in Iraq, and spelled out in detail how 96 percent of the money would be used.

The panel also required the administration to report to Congress on costs incurred for military activities and reconstruction of Iraq; the management of prisoners in Iraq and elsewhere; and the extent to which members of the selected reserve and National Guard are being "involuntarily ordered to active duty."

In its version of the $25 billion Iraq war fund, the Senate gave the administration a free hand to spend only $2.5 billion of the total.

Researcher Madonna A. Lebling contributed to this article.