By Steve Quinn
JUNEAU Alaska (Reuters) - Voting ended on Tuesday in a primary election in Alaska that has three Republicans, including a Tea Party candidate, vying for the chance to face a Democratic incumbent in a race seen as critical to their party's bid to regain control of the U.S. Senate.
The primary contest pits two former colleagues from Alaska's executive branch, Lieutenant Governor Mead Treadwell and ex-Natural Resources Commissioner Dan Sullivan, and the Tea Party's Joe Miller, against one another to decide who challenges Senator Mark Begich in November's general election.
All three positioned themselves as uniquely qualified to unseat the incumbent, who faces only a token, write-in opponent from New York in the Democratic primary.
Republicans need a net gain of six seats in the fall to retake a majority in the U.S. Senate.
"It's a nationally competitive seat, and it has a great deal of bearing on the state's representation" and its ability to advance local interests," said Jerry McBeath, a political scientist with the University of Alaska Fairbanks.
The high stakes have fueled a highly charged Republican contest, with campaign ads flooding the airwaves, websites and social media across this typically conservative-leaning state.
Republicans have long believed the seat belongs to them, especially since Begich claimed a narrow 2008 win a few weeks after a jury convicted former Senator Ted Stevens on federal corruption charges. That conviction was set aside before sentencing amid prosecutorial misconduct.
Sullivan is favorite in the polls, which have proven misleading in recent Alaska races. Still, he has raised more than $4 million, twice the amount of his two opponents combined, since launching his candidacy last fall.
Sullivan, who served as a U.S. Marine in Afghanistan and also as state attorney general under Governor Sean Parnell from 2009 to 2010, says he is taking nothing for granted.
He waged a simultaneous campaign against his primary opponents while trading punches with Begich in opposing television attack ads.
Many of the ads sought to portray the incumbent as close to Barack Obama and the president's policies in areas such as healthcare, a common refrain from all three Republican candidates.
"We are going after Mark Begich, his failed record," said Sullivan, who received the backing of former Secretary of State Condoleezza Rice and even a $1,250 donation from former President George W. Bush, for whom he once served as assistant secretary of state. "But we are defining ourselves with regard to my Republican primary opponents."
Treadwell says he welcomes his underdog status, and that he believes his 40 years of experience in Alaskan politics will help him prevail.
"What I hear from Alaskans is they are fed up with this kind of snowball fight between Mark Begich and Dan Sullivan," Treadwell said.
Miller, a Fairbanks attorney, is best known for his 2010 primary upset of U.S. Senator Lisa Murkowski, only to lose to her as a write-in candidate three months later.
Miller, who has the backing of former Alaska Governor Sarah Palin, said he does not believe he is the long shot some make him out to be. He cited the recent stunning upset of former House Majority Leader Eric Cantor to the Tea Party's Dave Brat in Virginia.
"Both of the other candidates are establishment candidates who will ultimately do what the ruling class asks them to do," Miller said. "They are part of the problem."
Jennifer Duffy, an analyst with the Cook Political Report in Washington, D.C., said Sullivan is the favorite in a tight, closely watched contest.
"The Republicans call this an opportunity, and Democrats pretty much say, 'Yeah.' They don't deny it," Duffy said.
Meanwhile in conservative Wyoming, which has three times as many registered Republicans as Democrats, Tuesday's primary sees incumbent Governor Matt Mead seeking re-election in a three-way race for the GOP nomination that includes the state's superintendent of public instruction and a retired physician.
(Reporting by Steve Quinn; Additional reporting by Laura Zuckerman in Salmon, Idaho; Editing by Daniel Wallis and Eric Walsh)