By Svea Herbst-Bayliss

BOSTON (Reuters) - Massachusetts Sen. Edward Kennedy, a leading liberal voice in the United States, had preventive surgery in Boston on Friday to unclog a partially blocked carotid artery in his neck and is expected to make a full recovery.

Dr. Richard Cambria made an incision in the 75-year-old Democrat's neck and removed plaque that was blocking more than 70 percent of his left carotid artery during the hour-long operation at Massachusetts General Hospital.

"There was a very high-grade blockage," Cambria said in a teleconference, adding that there is no indication at the moment that the right carotid artery is similarly blocked.

"The senator is eating ice cream and drinking ginger ale and looking forward to watching the Red Sox play this evening," Cambria said.

The blockage was discovered during a routine check of Kennedy's back and spine, doctors said, adding he is expected to make a full recovery.

A blocked carotid artery can lead to a stroke and death, doctors said.

Kennedy has suffered from back problems since a plane crash in 1964 in which the pilot and one of Kennedy's aides were killed and the senator was pulled from the wreckage with a back injury, punctured lung, broken ribs and internal bleeding.

The senior senator from Massachusetts will stay in the hospital overnight and resume his normal schedule after a brief recovery period, a Kennedy spokeswoman said.

The youngest brother of assassinated U.S. President John F. Kennedy, Kennedy was elected to the Senate in 1962 and currently serves as chairman of the Senate Committee on Health, Education, Labor and Pensions.

He helped win an increase in the national minimum wage this year and worked with Republicans to produce broad immigration reform, which failed in the Senate after stiff opposition from conservative Republicans.

(Additional reporting by Donna Smith in Washington)