WASHINGTON (Reuters) - Senator Mike Johanns, a Nebraska Republican, said on Monday that he would not seek re-election next year, becoming the fifth U.S. senator to announce plans to retire at the end of their current term.

A two-term Nebraska governor and former U.S. secretary of agriculture, Johanns, 62, was a freshman senator elected in 2008 for a six-year term.

"With everything in life, there is a time and a season," he said in a message Monday to Nebraskans co-signed by his wife, Stephanie. "At the end of this term, we will have been in public service over 32 years."

While his statement did not immediately tie the decision to partisan gridlock in Washington, he has voiced frustration in the past at Congress's inability to overcome stalemates on efforts to solve problems facing the United States.

He was the fifth senator in recent weeks - and the second Republican - to announce retirement plans ahead of 2014 elections. The others were Frank Lautenberg, an 89-year-old New Jersey Democrat; John Rockefeller IV, a West Virginia Democrat; Tom Harkin, an Iowa Democrat, and Republican Saxby Chambliss of Georgia.

(Reporting By Jim Wolf and Richard Cowan)