Story Highlights• NEW: Republican Sen. Jim Talent concedes in Missouri
• Democrat Jim Webb claims victory in Virginia but recount likely
• Montana Senate race too close to call with 66 percent of precincts reporting
• Republican Bob Corker projected to win Tennessee Senate race
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(CNN) -- Democrats are projected to pick up four GOP-held seats but must win the two remaining undecided races to gain control of the Senate.
Democratic candidates hold a lead in each of those two races -- in Virginia and Montana.
In Virginia, Democrat Jim Webb declared victory in his race against incumbent Republican Sen. George Allen early Wednesday, though a recount in the hotly contested election appeared likely.
"The votes are in, and we won," said Webb, who led Allen by nearly 12,000 votes with 99 percent of precincts reporting.
Allen assured supporters that "the counting will continue through the night."
In Montana, Republican Sen. Conrad Burns is trailing Democratic challenger state senator Jon Tester by about 7,000 votes -- or four percentage points -- with 66 percent of precincts reporting.
Incumbent Republican Sen. Jim Talent conceded the race in Missouri to Democrat Claire McCaskill saying, "the headwind was just very, very strong this year."
With 89 percent of precincts reporting, McCaskill -- who has served as state auditor since 1998 -- led the freshman senator by about 25,000 votes.
In Virginia, Webb led early returns, trailed Allen as more boxes came in and pulled ahead as late votes were counted.
Allen told supporters that he faced a recount in his first political race, winning by 18 votes.
Virginia does not conduct automatic recounts in close races, but the apparent loser can request one after the votes have been certified if the margin is less than one percent of the total votes cast.
CNN projects Democratic wins in Rhode Island, Pennsylvania and Ohio.
Republican Bob Corker, the mayor of Chattanooga, is projected to beat Democrat Rep. Harold Ford Jr. to claim the seat being vacated by Senate Majority Leader Bill Frist.
Ford cultivated a moderate voting record, but the African-American congressman faced a tough task in winning over conservative Republican voters in east Tennessee, especially in light of the Democrats' anemic record in the South over the last six years.
State treasurer Robert Casey Jr. is is projected to defeat Pennsylvania Sen. Rick Santorum, the third-ranking Senate Republican, and Democratic Rep. Sherrod Brown is projected to unseat incumbent Republican Sen. Mike DeWine in Ohio. (Hear DeWine's concession speech -- 3:39 )
Rhode Island's Sen. Lincoln Chafee, one of the few moderate Republicans in the Senate, is projected to lose to Democrat Sheldon Whitehouse, the former state attorney general. Though he has bucked the party line on some votes, Chafee -- whose father, John Chafee, held the seat for 20 years -- found the campaign trail difficult in the Democratic-leaning state.
In the current makeup of the Senate, Republicans hold 55 seats and Democrats control 44. Of the 33 seats up for re-election, the GOP is defending 15 of them and Democrats hold 17 seats.
Sen. Joe Lieberman, running as an independent after losing in the Democratic primary, is projected to win in Connecticut. (Watch Lieberman's victory speech -- 1:58 )
In New Jersey, Democratic Sen. Robert Menendez is projected to defeat Tom Kean Jr., and Maryland's Democratic Rep. Ben Cardin is projected to defeat Lt. Gov. Michael Steele, possibly ending Republicans' hopes of picking off two traditionally Democratic states.
Pennsylvania's Santorum, one of the most conservative Republican senators, consistently polled behind Casey throughout the summer. (Watch how Sen. Rick Santorum lost -- 4:01 )
"This just was a little too steep of a mountain to climb, but it was not for want of people helping us climb it," Santorum told supporters. (See Santorum's concession speech -- 2:42 )
In Ohio, controversies involving the state's Republican Party created a difficult political environment for DeWine, even though he was not connected to any of them.
"It just was not to be. This was not the year. We could not win," he said.
White House Press Secretary Tony Snow told CNN's Suzanne Malveaux the early results were not surprising and were keeping any eye on the Senate races in Montana and Missouri, where polls leading up to Election Night showed close races.
In other returns, CNN projects that independent U.S. Rep. Bernie Sanders will win the seat that Sen. Jim Jeffords of Vermont is vacating. Jeffords is the lone independent in the Senate, though he usually votes with Democrats.
Political observers expect Sanders to vote along the same lines as his predecessor.
Many Republican and Democratic incumbents were projected to cruise to easy wins. (Full Senate results)
CNN's Bill Schneider, Suzanne Malveaux, Dana Bash and John King contributed to this report.
Democrat Jim Webb, left, holds a slim lead over Sen. George Allen in Virginia. A recount looks likely.