Almost from the day he first arrived in 1979, Rep. Charles W. Stenholm (Tex.) has played a critical role as a Washington political middleman -- a centrist Democrat with an easygoing but tenacious manner who has helped presidents from Ronald Reagan to Bill Clinton pass key economic programs and grapple with the deficit.

Rep. Jennifer Dunn (R-Wash.), a consummate insider and peacemaker during the Republican Revolution of the 1990s, is one of the few women to serve on the Ways and Means Committee, and became an authority on tax policy and health care.

And Sen. John Breaux (D-La.), a political dealmaker with indefatigable energy and Cajun charm, helped pave the way for passage last year of President Bush's bill to restructure Medicare and add a prescription benefit.

As the 108th Congress comes to a close with a post-election "lame duck" session, Stenholm, Dunn and Breaux are among a significant number of major players departing the scene. Stenholm, for many years the leader of the centrist "Blue Dog" Democrats and a ranking member of the House Agriculture Committee, lost his West Texas House seat after falling victim to a GOP redistricting plan engineered by House Majority Leader Tom DeLay (R-Tex.). Dunn and Breaux are retiring from Congress to seek new careers.

More than four dozen House and Senate members are leaving Congress because of reversals at the polls, career changes or retirements. The departures, although not unusual in their number, strip Congress of some of its most experienced and skilled legislative operators, including both party leaders and unofficial dealmakers who sought common ground that would bridge often crippling partisan differences.

"The numbers themselves are modest, but it's quality that's lost," said Ross K. Baker, a political scientist at Rutgers University, who studies Congress. While Congress is an "extremely adaptable institution" with a constantly changing membership, it is losing some of its best bridge-builders as well as party leaders -- "a huge loss of experience and wisdom of people who know how to get things done," he said.

Thomas A. Daschle (S.D.), the Senate Democratic leader for the past decade, and Rep. Martin Frost (D-Tex.), a former chairman of the Democratic Congressional Campaign Committee, were defeated in the Nov. 2 election. Onetime House Democratic leader Richard A. Gephardt (Mo.), and Sens. John Edwards (D-N.C.) and Bob Graham (D-Fla.) gave up their seats to make bids for the White House. Republican Porter J. Goss (Fla.) left his House seat to run the CIA. Veteran Sens. Ernest F. Hollings (D-S.C.), Ben Nighthorse Campbell (R-Colo.) and Don Nickles (R-Okla.), and longtime Reps. Jack Quinn and Amo Houghton, both New York Republicans, Doug Bereuter (R-Neb.) and James C. Greenwood (R-Pa.) are retiring. Freshman Sens. Zell Miller (D-Ga.) and Peter Fitzgerald (R-Ill.) also are retiring.

When Nickles was elected to the Senate in 1980, he was 31, the youngest Republican ever elected to the chamber and a down-the-line conservative who rode into office on the same tide that elected Reagan. He intended to stay only a term or two, he recalls, but ended up remaining for four, including six years as GOP whip, the assistant leader.

Rep. George R. Nethercutt (R-Wash.), who toppled Democratic House Speaker Thomas S. Foley in 1994, lost his bid for the Senate. Ben Nighthorse Campbell (R-Colo.), the only American Indian in the Senate, cut a distinctive figure with his neck scarves, ponytail and motorcycle; he is retiring. Rep. Philip M. Crane (R-Ill.), a 17-term veteran, onetime presidential candidate and leader of the conservative wing of his party, was defeated by a Democrat who charged he was "a do-nothing congressman."

Norman Ornstein, who watches Congress from the American Enterprise Institute, said Congress was losing "some of its thoughtful institutionalists and centrists," such as Stenholm and Bereuter in the House and Breaux and Graham in the Senate. "Beyond loss of some iconic figures such as Gephardt, Daschle and to some extent Frost, the most significant is losing the core of Democratic centrists in both parties and the moving of the Republican Party ever more sharply to the right," he said.

Larry Sabato, director of the University of Virginia's Center for Politics, agreed and warned that the retirements and Election Day defeats of some veteran centrists will provide "more institutional polarization" within Congress -- with Republicans shifting more to the right and Democrats more to the left.

Emblematic of this change is the departure of Stenholm, 66, the son and grandson of Swedish farmers who was raised in the strict Luthern hamlet of Ericksdahl, Tex., 50 miles north of Abilene. Stenholm and other southern Democrats who arrived in Washington shortly before Reagan took office supported the new president's large supply-side tax cuts in return for promises of big spending cuts. But as the deficit continued to mount, Stenholm became the driving force behind a balanced budget amendment to the Constitution, which passed the House but foundered in the Senate.

He supported Clinton-era budget and economic policies that helped usher in the first budget surpluses in nearly 30 years. As ranking Democrat on the Agriculture Committee, he helped write the 2002 farm bill.

Stenholm sided with Democrats in 2001 to oppose Bush's proposed tax cuts, arguing that the drain on revenue could jeopardize Social Security and Medicare. Last year, he offered the Blue Dogs' budget on the House floor, which raised taxes by $129 billion over 10 years but also balanced the budget in eight years.

Stenholm went into the election at a severe disadvantage after a Republican redistricting plan threw him into a heavily GOP district, and Republicans cited the proposed tax increases to challenge Stenholm's conservative credentials and hammered him on abortion and same-sex marriage.

"I was painted as someone with no values, even though I'm pro-life and believe marriage should be between a man and woman," Stenholm recalled bitterly this week. "Yet, because I'm a Democrat, I was painted as someone I wasn't."

Stenholm's biggest regret? That he won't be around when Congress tries to "fix" Social Security.

Dunn, 63, a onetime IBM systems engineer and Washington state GOP chairman, was closely allied with former House speaker Newt Gingrich (R-Ga.), who helped her win a plum assignment to the Ways and Means Committee after the GOP takeover in 1994. She worked on the child support provisions of the welfare bill and pushed for medical savings accounts in the 1996 health care bill. She and Democrat Frost co-sponsored the Amber Alert legislation to encourage immediate response to reports of missing children.

Dunn aspired to be the first female House majority leader, but she faltered in her challenge to then-Majority Leader Richard K. Armey (R-Tex.) in 1998. Last January, following her marriage to a British-born businessman, Dunn announced that she was retiring from politics and would seek a new career. "It is time for me to move on," she wrote in a letter to supporters.

With the retirement of Breaux after 14 years in the House and 18 years in the Senate, Congress is losing one of its premier dealmakers, who worked assiduously with Republican as well as Democratic centrists to forge compromises on many of the top domestic issues of the day, including Social Security, Medicare and budget priorities.

Breaux, 60, said in an interview he feels he played a major role in passage of the Medicare drug benefit bill and tax legislation to increase investment incentives. But he was disappointed at inaction on Social Security. He was proud, he said, of the role he played with several Republicans, including the late Sen. John H. Chafee (R.I.) and now Sen. Olympia J. Snowe (Maine) in forming a centrist coalition within the Senate.

There are others to continue the work, including Democratic Sens. Joseph I. Lieberman (Conn.), Evan Bayh (Ind.), Mary Landrieu (La.), Blanche Lincoln (Ark.) and Ben Nelson (Neb.), Breaux said. But he worries about what he described as a "shift away from the center" in both houses of Congress.

Breaux plans to remain in Washington and enter the private sector, possibly as a lobbyist and consultant. He said he and Nickles have talked about a joint business venture.