Representative Rush D. Holt Jr. of New Jersey, a research physicist who became Congress’s chief advocate for scientific research over eight terms, announced on Tuesday that he is not seeking re-election this year.

Mr. Holt, 65, joins 12 fellow Democrats, and 21 Republicans, in an exodus from the House. But in an interview, he said he was not bemoaning what he acknowledged was “a certain level of dysfunction” in Congress.

“Congress, even with its frustrations, is the greatest instrument for justice and human welfare in the world,” he said. “The stories trying to puzzle out why someone would do something else are based on this rather narrow way of thinking that the only purpose for a member of Congress is to be re-elected. I’ve never viewed it that way, and I think everybody who’s worked with me knows that I think there are a lot of things that I can and should be doing.”

Mr. Holt’s retirement is not expected to affect the Democrats’ chances in 2014; a seat that he barely wrested from a Republican in 1998 has been made reliably Democratic in two rounds of redistricting.