WASHINGTON — Another U.S. senator will retire.

Sen. Jeff Bingaman, D-N.M., intends to retire at the end of his term, his office announced today, the latest in a string of departures to hit the Democrats as they look ahead to the 2012 elections.

A formal announcement was expected later today, added an aide, Jude McCartin.

Bingaman, 67, was first elected to his seat in 1982.

He is the third Democrat and sixth member of the Senate to decide to step aside at the end of their current terms.

The others are Democratic Sens. Kent Conrad of North Dakota and Jim Webb of Virginia; Republicans Kay Bailey Hutchison of Texas and Jon Kyl of Arizona; and independent Sen. Joseph Lieberman of Connecticut.

Democrats hold a 53-47 majority, including two independents who side with them. But they must defend 21 of the 24 seats on the ballot next year, and face a struggle to retain control.