For a decade, the face of Senate Democrats has been a short, mild-mannered man who fought with deceptive toughness behind the scenes against the agenda of Republicans.

On Tuesday, however, voters in South Dakota ended the Senate career of Minority Leader Thomas A. Daschle (D), forcing Democrats to find new leadership even as they reeled from a series of Election Day defeats that increased the GOP's majority in the 100-seat Senate from 51 to 55.

Moving quickly to fill the vacuum yesterday, Minority Whip Harry M. Reid (D-Nev.) announced that he would seek to move up to Daschle's position. A spokesman said Reid had enough votes among the Senate's 44 remaining Democrats to win. Late yesterday, Sen. Christopher J. Dodd (D-Conn.), who had been seen as Reid's only potential challenger, said he would not run and will support Reid.

Daschle's sudden fall came as a shock, even though his race for a fourth term against Republican John Thune had been considered too close to call for weeks. He was the first Senate leader to be defeated since 1952, when Democratic Majority Leader Ernest W. McFarland of Arizona was unseated by Republican Barry Goldwater.

Daschle, 56, became the third South Dakota senator since 1980 to be turned out of office when seeking a fourth term. The others were Sens. George McGovern (D) and Larry Pressler (R).

For the minority leader's supporters, it was little solace that the defeat came as part of a broader electoral realignment in the Senate, in which Democratic candidates were beaten in nearly every close election across the South and Great Plains, where GOP strength has been growing. Some supporters wept and cheered simultaneously at an emotional rally early yesterday in Sioux Falls at which Daschle conceded defeat. "I like sunrises better than sunsets," he admitted.

Although Daschle was pilloried by his Republican rival as the Senate's leading "obstructionist," one Senate GOP leader spoke almost sympathetically yesterday of the political plight of the Democrats' fallen leader.

"Personally, he was a very nice guy, easy to deal with," said Senate Majority Whip Mitch McConnell (R-Ky.). "He was in a very difficult spot. He had to represent a state that was significantly to his right, and he could do so as long as he didn't have a strong opponent. He was caught between his job as principal opponent to the president and trying to be something else in South Dakota."

In his nearly 10 years as Democratic leader, Daschle shaped and reflected the consensus of his caucus and, in doing so, enjoyed the strong support of his Democratic colleagues. When he employed tactics that Republicans labeled as obstructionist -- such as Democratic filibusters against some of President Bush's judicial nominees and Democratic criticisms of the handling of the Iraq war -- it was usually at the behest of his caucus.

Democrats controlled the Senate only briefly during Daschle's tenure, in part of 2001 and 2002. During President Bill Clinton's terms, he helped steer major trade legislation, welfare reform, Medicaid reform and income subsidies to the working poor through the tax code. But his major accomplishments, according to spokesman Dan Pfeiffer, involved South Dakota.

Legislation he sponsored helped create the state's burgeoning ethanol industry, a major economic boon to corn growers. He also sponsored rural water projects that were of crucial importance to South Dakota's recreation industry and environment.

Reid, 55, his likely successor, handily won reelection Tuesday after narrowly escaping defeat six years earlier. He came to the Senate with Daschle in 1987 and became his trusted ally.

He has a reputation as a savvy legislative operator. "He's very tough, and I have a lot of respect for him," said Sen. John Cornyn (R-Tex.).

McConnell said he has had "excellent relations" with Reid, the opposing whip. But he added that it was wrong to assume Reid would be less tough than Daschle in dealing with the Republicans.

Researcher Carmen Chapin contributed to this report.

Daschle supporters comfort each other after he conceded the race in Sioux Falls, S.D.Senate Minority Leader Thomas A. Daschle lost in his bid for a fourth term.As Sen. Daschle talks to a supporter, his brother Chuck hugs the senator's wife, Linda, holding granddaughter Eva.Minority Whip Harry M. Reid said he will seek Daschle's post.