Sen. Carl Levin (D-Mich.), a veteran Jewish lawmaker who for years was a major influence in defense policy, will not seek reelection.
Levin, 78, was quoted Thursday by The Associated Press as saying that his decision was "extremely difficult" but that he wanted to serve out the remainder of his term, which ends in 2014, without "distraction."
Levin heads the Senate's Armed Services Committee, and in that capacity has been influential in defense policy, helping to maintain record levels of defense assistance for Israel.
More recently, he led the pushback against claims that President Obama's nominee for defense secretary, Chuck Hagel, was not sufficiently pro-Israel or supportive of tough anti-Iran measures for the job.
Levin's public dressing-down of Hagel's sharpest critic on the committee, Sen. Ted Cruz (R-Texas), for suggesting without evidence that Hagel had received favors from rogue states, helped turn the tide for the nomination, which ultimately was approved.
First elected in 1978, Levin is Michigan's longest-serving senator.
Levin's brother, Sander, is the top Democrat on the U.S. House of Representatives tax-writing Ways and Means Committee.