By Kay Henderson

DES MOINES (Reuters) - Senator Tom Harkin, a veteran Iowa Democrat and one of the most liberal senators, said on Saturday he will not seek re-election in 2014, putting at risk what was considered a safe Democratic seat.

Harkin, 73, who has focused much of his nearly 40-year congressional career on farm policy, education and expanding rights for people with disabilities, is the third senator facing re-election next year who has announced his retirement, following Democrat Jay Rockefeller of West Virginia and Republican Saxby Chambliss of Georgia.

"It's somebody else's turn. It's time for me to step aside ... . I think that's not only good for our party, it's good for our state and for our nation," Harkin said in an interview with Reuters.

He said he had no health problems but had promised his wife that he would quit before it was too late to enjoy other things in life.

Iowa, site of the country's first presidential nominating contest, is considered a political swing state. Republican Charles Grassley is Iowa's other U.S. senator.

In remarks to the Iowa Democratic Party central committee after his announcement, Harkin said he would stay politically active.

"I'm not quitting today. This is not a time for legacy talks or anything like this," said Harkin, who has served in Congress since 1974.

Several committee members had tears running down their cheeks as he spoke.

President Barack Obama, a fellow Democrat, praised Harkin for his decades of public service.

"During his tenure, he has fought passionately to improve quality of life for Americans with disabilities and their families, to reform our education system and ensure that every American has access to affordable health care," Obama said in a statement.

Senate Majority Leader Harry Reid, a Nevada Democrat, in a statement described Harkin as "a passionate progressive, whose deeply held principles have provided a guiding light to Democrats for decades."

SEARCH IS ON

Party officials said Harkin's announcement, coming early in the current two-year election cycle, provides ample time to recruit a strong Democratic candidate.

Among Democrats, U.S. Representative Bruce Braley is widely seen as a front-runner. U.S. Agriculture Secretary Tom Vilsack, a former Iowa governor, and his wife, Christine Vilsack, who ran unsuccessfully for Congress last year, are also viewed as potential candidates. Continued...