Baucus, 64, will preside over domestic issues that the White House regards as crucial, including tax policy and the future of the fragile Social Security system. Baucus, sometimes to the consternation of his fellow Democrats, has a tradition of working closely with his Republican colleagues on major...

Biden, 63, has chaired the Foreign Relations Committee once before and is the leading Democratic voice on foreign policy. Elected to the Senate at 29, he has spent most of his adulthood on Capitol Hill.

Bingaman, 63, likes to operate behind the scenes and shuns national publicity.

Rockefeller, 69, was elected to the Senate in 1984 and became vice chairman of the intelligence committee three years ago. He voted for the Iraq war resolution but later said he regretted it.

Leahy, 66, has been steeped in some of the Senate's most polarizing debates of recent years, including nominations to the federal courts and anti-terrorism legislation.

One of the Senate's most liberal members, Boxer, 65, has been a champion of environmental causes. She has been a leader of the Democrats' efforts to block drilling in the Arctic National Wildlife Refuge. She has pushed for stiffer drinking-water standards and lower emissions of toxic substances...

Byrd, 88, is the longest-serving member of the Senate. This will be his third stint as chairman of Appropriations, which he joined in 1959. He also served two terms as majority leader.

A fierce opponent of budget deficits, Conrad, 58, has been a persistent critic of the Bush administration's fiscal policies. His Senate Web site features a chart library, containing scores of graphs and tables, some titled "The Wrong Priorities," that Conrad uses to illustrate his dim view of the...

Harkin, 66, is a Capitol Hill veteran of three decades who has been a leading voice for farmers and people with disabilities.

Levin, 72, is a vocal critic of the Bush administration's handling of the war in Iraq. In June, he tried unsuccessfully to pass a nonbinding proposal urging President Bush to begin withdrawal of troops from Iraq by the end of this year.

Inouye, 82, the first Japanese American to serve in Congress, began his political career before Hawaii became a state. He was elected to the territorial legislature in 1954 and was sent to Congress in 1959, serving first in the House and later in the Senate.

Dodd, 62, is the ranking Democrat on the Rules and Administration Committee but is likely to sacrifice that chairmanship to assume the top slot on the banking committee. That would have gone to Democrat Paul S. Sarbanes (Md.), 73, but he is retiring in January.

At 74, Kennedy has served in the Senate for 44 years -- the third-longest tenure in U.S. history -- and is the body's most enduring liberal. The younger brother of President John F. Kennedy -- and once a presidential candidate himself -- he has long been the patriarch of a family of extraordinary...

Lieberman, 64, is the first senator in modern times to win a general election after losing a party primary -- let alone to claim a chairmanship right afterward. The vice presidental running mate to Al Gore in 2000, Lieberman won as an independent after his defeat in the primary by Connecticut...

Aging, Herb Kohl (Wis.); Indian Affairs, Byron L. Dorgan (N.D.); Rules and Administration, Dianne Feinstein (Calif.); Small Business and Entrepreneurship, John F. Kerry (Mass.); Veterans' Affairs, Daniel K. Akaka (Hawaii).

Conyers, 77, is the second-longest-serving House member. In August, Conyers and the minority staff of the committee released a lengthy report, "Constitution in Crisis," that detailed what they said were 26 laws and regulations that President Bush has violated. That prompted Republicans to hint that...

Dingell, 80, has spent nearly 51 years in the House and was chairman of the Energy and Commerce Committee for 14 years.

Lantos, 78, was born and raised in Hungary and is Congress's only Holocaust survivor.

Hastings, 70, is the leading candidate for chairman of the committee.

Oberstar, 72, has been hanging around the committee since the 1960s, when he was chief aide to fellow Minnesotan John A. Blatnik, the chairman of what was then called the Public Works and Transportation Committee. Now, the low-key legislator from the Iron Range has a chance to run the place.

Frank, 66, an openly gay man, is a leader of the liberal wing of the House Democrats and was elected in 1980. Under his leadership, the committee will almost certainly change gears to focus less on Wall Street and more on the social-policy issues under the panel's purview, especially expanded availability of affordable housing....

Waxman, 67, will try to reinvigorate oversight of the executive branch.

Skelton, 75, has represented west-central Missouri for 30 years, a district that includes Harry S. Truman's birthplace and two major military bases: Fort Leonard Wood and Whiteman Air Force Base.

Miller, 61, is a Bay Area liberal, a labor booster and one of the closest allies of Rep. Nancy Pelosi, soon to be the House speaker.

Spratt, 64, is a courtly Southerner and a wonkish moderate from an old South Carolina family. A graduate of Yale and Oxford, he has a reputation as a hard worker.

Rangel, 76, is one of the most fiery members of the House and soon will be one of the most powerful, leading the panel that sets tax and trade policy and presides over Medicare and Social Security.

Thompson, 59, has been in public office since he was 21 years old, when he was elected alderman in his rural hometown of Bolton.

Peterson, 62, won a House seat in 1990 on his fifth try. He opposes abortion rights and gun control, generally supports labor unions and farm subsidies, and opposed President Bill Clinton on his 1993 budget, NAFTA and normal trade relations with China. He co-founded the "Blue Dog" coalition of conservative Democrats....

Obey, 68, was chairman of the committee briefly before the 1994 GOP takeover.