Last week, as a federal grand jury approached the end of its investigation of senior officials in the Bush White House, Sen. Chuck Hagel of Nebraska quietly introduced two far-reaching pieces of legislation dealing with such serious national problems as immigration, Medicare, Medicaid and Social Security.

It may have been just a coincidence that Hagel moved to raise his profile on these topics just as special prosecutor Patrick Fitzgerald was winding up his two-year examination of leaks from the staffs of the president and vice president concerning the identity of a covert CIA operative.

But if you are looking for signs of the changing political environment in Washington and the Republican Party, Hagel's Halloween-festooned office is the right place to begin.

A reflective student of political trends here and abroad, as well as a skilled politician who has won two Senate terms without breaking a sweat, Hagel, 59, is one of many Republicans weighing the odds for the 2008 presidential contest.

Like such colleagues as George Allen of Virginia and Sam Brownback of Kansas, or such governors as Mitt Romney of Massachusetts and Mike Huckabee of Arkansas, Hagel barely registers in the national polls because he is largely unknown outside his home state.

As he readily acknowledged in an interview, his friend John McCain, the man he supported for the nomination in 2000, is far out front in popular support, thanks to the enduring legacy of that earlier campaign.

But McCain carries the scars of that bruising primary battle against Bush in 2000, and his reputation as a maverick makes him perhaps more appealing to independents and Democrats than to Republicans. McCain will also be 71 when 2008 rolls around.

As Hagel said, "No one knows what the country -- or the party -- will be looking for when we get ready to choose a new president."

What is clear is that the Bush White House would be unlikely to view Hagel as its preferred successor. His loyalty to the president is measured by his 94 percent support score on roll-call votes in 2004, two points higher than that of Majority Leader Bill Frist in the Congressional Quarterly ratings.

But he has dissented publicly on major issues. While he voted to authorize the use of force in Iraq, he has been strongly critical of the prewar intelligence, the military planning and the management of the war. On the president's landmark initiative to add prescription drug coverage to Medicare, Hagel voted no, arguing that the cost of the new entitlement had not been accurately estimated or adequately financed.

A classic business-oriented conservative, with limited liking for the social issues of the religious right, Hagel argues that the preoccupation with "satisfying the base" has meant, "no question, the Republican Party has become captive to extreme right-wingers."

Were President Bush still riding high, were the Karl Rove strategy of mobilizing every possible vote on the right the accepted wisdom for 2008, Hagel's views might well be regarded as heresy.

But he thinks -- and he has lots of company among independent pollsters and operatives -- that the public mood is shifting and there is a growing demand for what he calls "responsible governance."

That's not easily defined, but one characteristic, Hagel says, is clearly the search for a consensus that commands more than a partisan majority of 51 percent.

It also means stepping up to the largest challenges, rather than postponing or finessing them. Thus, in the area of entitlements, Hagel wants to drum home the message that the three big ones -- Social Security, Medicare and Medicaid -- represent a $42 trillion unfunded commitment over the next 75 years, something that threatens the well-being of more than two generations.

Rather than offering patchwork remedies, Hagel and Rep. John Tanner, a Tennessee Democrat, are sponsoring legislation to create a small, bipartisan commission to look at the challenge in its entirety. The makeup of such a group will be a topic when Hagel meets this week for one of his periodic sessions with retiring Federal Reserve Chairman Alan Greenspan.

On immigration, where Hagel teamed in the last Congress with former Senate Democratic leader Tom Daschle, he has a package of proposals addressing border security, employment rights and the integration of undocumented workers and their families into local communities. His bills will probably be on the Senate agenda next year.

Hagel's concepts can sometimes be murky, as when he describes his hopes for a U.N.-sanctioned peace and security conference on Iraq. But as the post-Bush period of Republican history begins to come into focus, there will be more room for independent thinking of the kind Hagel loves to offer.