WASHINGTON (Reuters) - Democratic Senator Tom Harkin of Iowa said on Saturday he will not seek re-election in 2014, saying he felt that after 40 years in Congress, it will be "somebody else's turn."

Harkin, 73, is one of the most liberal senators and has focused much of his long congressional career on farm policy and legislation aiding people with disabilities.

Iowa, site of the early presidential caucuses, is considered a political swing state, putting Democrats' long-held Senate seat at risk. Republican Charles Grassley is Iowa's other U.S. senator.

"I don't by any means plan to retire completely from public life at the end of this Congress," Harkin said in a statement. "But I am going to make way for someone new in this Senate seat. I think that is right not just for me, but for Iowa, as well."

In his remaining two years in office, Harkin said he will focus on implementing President Barack Obama's healthcare reforms, expanding job opportunities for people with disabilities and expanding access to education.

Harkin was first elected to the House of Representatives in 1974 and the Senate in 1984.

"When the current Congress is over, I will have served in the United States House of Representatives and the U.S. Senate for a total of 40 years. After 40 years, I just feel it's somebody else's turn," he said.

(Reporting by Richard Cowan and Vicki Allen; Editing by Doina Chiacu)