Republicans appeared certain to retain control of the U.S. Senate early Wednesday after pulling off key wins in the South, and they had the prospect of widening their current narrow margin by winning several Senate races that were still undecided.

Democrat Barack Obama's landslide in Illinois, putting a formerly Republican seat in the Democratic camp, was more than offset when the GOP picked up seats in South Carolina, North Carolina, Georgia and Louisiana, while fending off fierce Democratic challenges to Republicans in Oklahoma and Kentucky.

In North Carolina, Republicans dealt a particularly symbolic blow to Democrats, as GOP Rep. Richard Burr defeated Democratic Erskine Bowles for the seat now held by Democratic vice presidential nominee John Edwards. Trailing for much of the campaign to Bowles, who had served as chief of staff to President Bill Clinton, Burr went on the attack and overcame Bowles' lead with the help of a burst of GOP advertising in the campaign's final weeks.

Daschle struggles in race

Senate Minority Leader Tom Daschle (D-S.D.), a prime GOP target, was in an urgent fight early Wednesday morning to hold his seat. If Daschle loses, it would be the first defeat for a Senate party leader since 1952 and would remove the highest-ranking Democrat in the country.

In Louisiana, Republican Rep. David Vitter pulled off a surprise by winning a majority over his competitors and avoiding a Dec. 4 runoff for the seat held by retiring Democratic Sen. John Breaux. Louisiana is the only state in which candidates face a runoff if no one wins a majority on Election Day.

Regardless of who occupies the White House, continued Republican control of the Senate and House will be a crucial benefit to the GOP in deciding what kind of legislation is considered by Congress in the next administration. Republican domination will also give the party exclusive control over investigations that may arise over Iraq or any potential controversies.

Democrats had entered the contest for control of the Senate in a more difficult position than the GOP, because more of their incumbents were retiring. Republicans started the evening with a 51-48 majority in the Senate, with independent Sen. Jim Jeffords of Vermont generally voting with the Democrats.

The Democrats gained some good news in Colorado, where Ken Salazar was elected over brewery magnate Peter Coors, a Republican. The seat had been held by retiring Sen. Ben Nighthorse Campbell.

Salazar becomes the first Hispanic U.S. senator in more than 25 years.

Still undecided was a key race in Alaska, where Democrats hoped to pick up another seat. But Democrats also had to defend a seat in Florida, as well as Daschle's in South Dakota.

Given the results, Sen. Dick Durbin (D-Ill.) predicted continued political polarization in Washington. "It means more of the same, I'm afraid," Durbin said.

Shortly before midnight, Senate Majority Leader Bill Frist (R-Tenn.) predicted Republicans would pick up two to four seats in the Senate. "It looks like we'll have, possibly and probably, a clean sweep through the South," Frist said on NBC.

In the House, Republicans also appeared certain to retain control. Republicans currently hold a 227-205 edge in the chamber, and only three dozen races were considered competitive. In a rare upset, Democrat Melissa Bean appeared to unseat Rep. Phil Crane (R-Ill.), the longest-serving Republican in the House.

The GOP was assisted in House races by a controversial redistricting plan in Texas engineered by House Majority Leader Tom DeLay (R-Texas). It re-drew electoral boundaries in a way that was likely to tip five Democratic-held districts toward a Republican majority.

4 Texas Democrats lose

Republicans had defeated four veteran Texas Democrats by late Tuesday: Reps. Charles Stenholm, a leading fiscal conservative, Martin Frost, a former member of the party's congressional leadership, Max Sandlin and Nick Lampson.

Nick Clooney, a former Cincinnati television anchor and father of actor George Clooney, lost his bid to keep an open seat in Democratic hands.

In the Senate, South Carolina three-term Republican congressman Jim DeMint won the seat vacated by Democratic Sen. Ernest "Fritz" Hollings, a 38-year Senate veteran. DeMint bested Democrat Inez Tenenbaum, the state's superintendent of education, in a tight race.