J. Scott Applewhite/AP Photo

Sen. Thad Cochran, R-Miss., said today he intends to seek re-election in 2014, setting up one of the biggest Republican primaries pitting the establishment vs. the tea party in the country next year.

"Our nation and the State of Mississippi continue to face many challenges and opportunities. We must work to defend our national security interests, roll back burdensome policies like Obamacare, continue the fight to reduce our national debt and create opportunities for more jobs and economic growth," Cochran said in a statement today. "I will run for re-election to the United States Senate. I will run hard and be successful so that I can continue to serve the people of Mississippi and our nation effectively."

Cochran, who turns 76 this weekend, will run to secure his seventh term in the Senate, but he enters a race against Mississippi state Sen. Chris McDaniel, who has picked up the endorsement of several national tea party-leaning groups.

Mississippi is a solidly red state, but the race between a nearly 36-year veteran of the Senate and the tea party-backed newcomer will become one of the most closely watched Republican races in the country.

McDaniel, 41, entered the race in October and quickly was endorsed by the Senate Conservatives Fund and Club for Growth, who reiterated its support for McDaniel today.

"Throughout his over forty years in Washington, Senator Thad Cochran has done some good things for Mississippi, but he's also done some bad things," said Chris Chocola, president of the Club for Growth. "Fortunately, Republicans in Mississippi have a real choice for the United States Senate this year. They can vote for Senator Cochran, or they can vote for a more fiscally conservative alternative who is dedicated to limited government and passing policies that will increase economic growth."

But Cochran, who has not faced a tough challenger since joining the Senate in 1978, has the support of much of the Republican establishment, who up until today were uncertain if he would seek a seventh term.

"I think people are relieved that he's running," Henry Barbour, a major state lobbyist and a national committeeman for the Republican National Committee, told ABC News. "I certainly will do all I can to help him. We need more people in Washington who understand how to work with people. They are just few and far between these days."

Cochran is the second-longest serving Republican in the Senate today. He is also a top member of the Senate Appropriations Committee, a powerful panel that allocates money to federal agencies and departments. Cochran chaired the committee between 2005 and 2007 when Mississippi was recovering from Hurricane Katrina and helped secure billions of dollars for coastal communities ravaged by the storm.

But there is a push among some conservatives to unseat incumbent senators who they believe are too entrenched in the politics of Washington, D.C., a factor McDaniel and his supporters will likely try to highlight in the June primary. McDaniel's campaign welcomed Cochran to the race today.

"Sen. Cochran has had a long and distinguished career representing the people of Mississippi," McDaniel said in a statement. "I look forward to a positive campaign based on the future of our state, our country and the Republican Party. As a strong conservative, I will fight to bring those values to Washington."