By Suzi Parker
Little Rock, Arkansas (Reuters) - Arkansas Representative Tom Cotton, a rising star in the Republican party serving his first term in Congress, will run against Democratic U.S. Senator Mark Pryor in what is likely to be one of the most hotly contested 2014 election races, a Republican source said on Wednesday.
Cotton, 36, scheduled an event in his hometown of Dardanelle for August 6 to announce his challenge to the moderate Pryor, one of the most vulnerable Democratic incumbents in the Senate.
Cotton's staff declined comment on what he would say at the event, but a Republican source with direct knowledge said Cotton would announce a run for the Senate.
"On Tuesday Tom is inviting his hometown and all who have supported him along the way to hear about his fight to represent Arkansas's values in D.C.," Caroline Rabbit, Cotton's spokeswoman, said in an email. "He looks forward to sharing his plans to continue that fight in the coming year."
Cotton had been the favored Arkansas candidate of national Republicans trying to recruit a strong 2014 slate in a bid to win majority control of the U.S. Senate. Republicans need to gain six seats in the 2014 midterm elections to seize the majority from Democrats and control the agenda in the chamber.
Republicans have a good shot at winning open seats left by retiring Democrats in West Virginia, South Dakota, and Montana. They need to knock off some incumbents in Republican-leaning states such as Alaska and Louisiana as well as Arkansas.
Pryor, 50, the son of former Arkansas U.S. Senator David Pryor, has a moderate voting record in Washington.
Arkansas has moved steadily to Republicans in recent years despite being the home state of former Democratic President Bill Clinton. President Barack Obama lost the state in the 2012 election and Republicans won majority control of the state legislature.
While he has not completed his first term in Congress, Cotton is an articulate veteran of the Army, serving in the Iraq and Afghanistan wars, who has been given an unusually prominent role in foreign-policy debates in the U.S. House of Representatives for a new member.
There have been no independent opinion polls before the formal start of the Arkansas Senate. A Republican group, the Senate Conservatives Fund, published a survey at the end of June that showed Pryor with 41 percent and Cotton 40 percent, and 19 percent undecided. The survey of 600 likely voters had an error margin of plus or minus 4 percent.
Jay Barth, a political science professor at Hendrix College in Conway, said Arkansas was "about to see more spending than the state has ever seen in a political race."
More than a year before the election, groups on both the political right and left have been advertising in Arkansas, including the conservative Club for Growth and New York Mayor Michael Bloomberg's gun-control group, Mayors Against Illegal Guns.
"Today's news comes as absolutely no surprise as Cotton's visibility nationally and strong fundraising numbers have indicated his preparation for the race," Barth said.
Pryor immediately issued a statement criticizing Cotton.
"In seven short months, Tom Cotton's reckless and irresponsible voting record has alienated Arkansas farmers, seniors, students, women, parents and the business community by voting against such measures as the Farm Bill, student loans, the Violence Against Women Act, and trying to cut Social Security and Medicare," Pryor campaign manager Jeff Weaver said.
(Reporting by Suzi Parker in Little Rock; Writing by Greg McCune; Editing by Dan Grebler and Prudence Crowther)