(Reuters) - Virginia Republican George Allen easily won his primary race on Tuesday in the first step of his bid to reclaim the U.S. Senate seat he narrowly lost in 2006, as voters in four states set the stage for hotly contested battles that could shift control of the Senate.
Allen, also a former Virginia governor, lost by barely 9,000 votes in 2006 to Democrat Jim Webb, who is retiring at the end of his term next year. In the November 6 elections, Allen will face another ex-governor, Tim Kaine, who was unopposed for the Democratic nomination.
Republicans need a net gain of four seats in November to take control of the U.S. Senate.
Besides Virginia, voters in Maine, North Dakota and Nevada were picking Senate candidates in contested primaries on Tuesday.
Allen, once a rising star on the national political stage who stumbled in his 2006 re-election bid on the issue of race, took 65 percent of the vote. Jamie Radtke, the strongest of his three rivals, trailed with just over 23 percent.
Allen and Kaine both enjoy significant fundraising capability, well-established campaign networks and national prominence. Allen weighed a presidential run four years ago. Kaine was an early backer of President Barack Obama and later served as Democratic National Committee chairman.
Virginia is considered a tossup in the 2012 presidential election, ensuring the Allen-Kaine campaign will carry added significance.
In Maine, voters were picking candidates for the open U.S. Senate seat being vacated by Republican Olympia Snowe, who is retiring.
INDEPENDENT FAVORITE IN MAINE
Cynthia Dill, a civil rights lawyer and state senator, won the Democratic nomination. With 75 percent of precincts reporting, Republican Charles Summers, Maine's secretary of state and a former Snowe aide, had a 6-point lead over his nearest challenger.
Both Dill and her Republican rival, however, will face an uphill task running against early favorite Angus King, a popular former two-term governor and independent.
In the Republican primary for North Dakota's open Senate seat, the state's lone U.S. representative, Rick Berg, was leading Duane Sand by 67 percent to 33 percent with nearly 47 percent of precincts reporting. The victor will face Democrat Heidi Heitkamp, a former state attorney general, who was unopposed in her party's primary.
Veteran Democratic Senator Kent Conrad has opted not to seek re-election in North Dakota, which leans heavily Republican in its legislature and has a Republican governor.
In Nevada, seven-term U.S. Representative Shelley Berkley faces little serious competition in her race to become the Democratic nominee to challenge Republican Senator Dean Heller, who was appointed last year after John Ensign resigned in disgrace following a sex scandal.
Heller, like Berkley, was expected to easily win his party's nomination, setting up a general election race that will help decide whether the Nevada's senior U.S. senator, Democrat Harry Reid, remains majority leader.
But the most hotly contested Nevada primary on Tuesday was for the newly created, Democratic-leaning 4th Congressional District, where three candidates were in a close race for the Republican nomination to run against the likely Democratic nominee, state Senate Majority Leader Steven Horsford.
Businessman Danny Tarkanian had strong support from the Tea Party movement and the most name recognition in the Republican field as the son of former University of Nevada, Las Vegas, basketball coach Jerry Tarkanian. But he faced a tough race against state Senator Barbara Cegavske and businessman Dan Schwartz.
There was controversy in South Carolina, which did not have a U.S. Senate seat to contest in its primary on Tuesday, after the state Supreme Court removed more than 200 contenders for other offices from the ballot on grounds that they had improperly filed paperwork for their candidacies.
Incumbent U.S. Representative Joe Wilson, known for shouting "You lie!" during President Barack Obama's 2009 State of the Union address to Congress, won the Republican primary and is running unopposed for re-election in November.
In another closely watched race, nine Republicans and four Democrats were seeking their parties' respective nominations for newly established 7th congressional seat in South Carolina.
(Additional reporting by Ros Krasny, John Crawley, Steve Gorman and Harriet McLeod; writing by David Bailey; editing by Mohammad Zargham)