CUMMING, Iowa – A prominent liberal Democratic senator said Saturday he will not seek a sixth term in 2014, a decision that eases some of the burden the national Republican Party faces in regaining control of the Senate.

Iowa Sen. Tom Harkin, chairman of an influential Senate committee, announced his decision during an interview with The Associated Press, and said the move could surprise some.

But the 73-year-old cited his age — he would be 81 at the end of a sixth term — as a factor in the decision, saying it was time to pass the torch he has held for nearly 30 years, freeing a new generation of Iowa Democrats to seek higher office.

“I just think it’s time for me to step aside,” Harkin told the AP.

Democrats hold a 55-45 advantage in the Senate, requiring Republicans to gain six seats to win back the chamber. But Democrats have more seats to defend in 2014_20 compared to only 13 for Republicans.

Harkin, first elected in 1984, ranks 7th in seniority, and 4th among majority Democrats. He is chairman of the health, education, labour and pensions committee, and chairman of the largest appropriations subcommittee.

He has long aligned with the Senate’s more liberal members, and his signature legislative accomplishment is the 1990 Americans with Disabilities Act. He also served as a key salesman of President Barack Obama’s 2010 health care bill to the wary left.

“I’m not saying that giving this up and walking away is easy. It’s very tough,” Harkin said at his rural Iowa home south of Des Moines. “But I’m not quitting today. I’m not passing the torch sitting down.”

Harkin’s news defied outward signals. He has $2.7 million in his campaign war chest, second most among members nearing the end of their terms, and was planning a gala fundraiser in Washington, D.C., next month featuring pop star Lady Gaga.

Obama released a statement saying Harkin will be missed and thanking the senator for his 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.

Although members of his family have been diagnosed with cancer, Harkin said his health is good — and reported a recent positive colonoscopy. But he said “you never know,” and that he wanted to travel and spend his retirement with his wife Ruth “before it’s too late.”

But by opening a door in Iowa, Harkin has created a potential headache for his party nationally in keeping control of the Senate.

Democrats likely would have had the edge in 2014 with the seat, considering Harkin’s fundraising prowess and healthy approval rating. A poll by the Des Moines Register taken last fall showed a majority of Iowans approved of his job performance.

Democrats hold a 55-45 advantage in the Senate, requiring Republicans to gain six seats to win back the chamber. But Democrats have more seats to defend in 2014 — 20 compared to only 13 for Republicans. Historically, the president’s party loses seats in the midterm elections after his re-election.

In Republican-leaning West Virginia, five-term Democratic Sen. Jay Rockefeller recently announced he would not seek re-election. And on Friday, Georgia Sen. Saxby Chambliss, a Republican, announced that he wouldn’t seek a third term.

Democratic incumbents also face tough re-election races in Arkansas, Louisiana, Montana, North Carolina and Alaska — all states carried by Republican presidential nominee Mitt Romney in November’s presidential election.

Harkin’s move creates a rare open Senate seat in Iowa. Harkin, Iowa’s junior senator, is outranked by Sen. Charles Grassley, who has held the state’s other seat since 1980.

Attention will turn immediately to U.S. Rep. Bruce Braley, a fourth-term Democrat from Waterloo, long mentioned as a possible Harkin successor. Braley, who was travelling in Iowa on Saturday, did not immediately return requests by the AP for comments beyond an emailed news statement calling Harkin a “mentor” and “progressive force” who leaves “a legacy few will ever match.”

Although no Republicans have stepped forward, Harkin’s news gives the party’s private huddles new life.

U.S. Rep. Tom Latham is a seasoned Republican congressman, a veteran appropriations committee member and a robust fundraiser who has survived challenges to win 10 consecutive terms. Aides to Latham declined to comment beyond issuing a statement saying the congressman “respects Sen. Harkin’s decision (and) looks forward to continuing to work with him.”