Senator Joseph R. Biden Jr. underwent surgery today to correct an aneurysm in an artery that supplies blood to the right side of the brain, a spokesman for the Walter Reed Army Medical Center said.

The spokesman, Peter Esker, said Senator Biden was awake, resting comfortably and talking with his family after the operation, his second this year to correct an aneurysm. An aneurysm is a ballooning of an artery.

The 4 1/2-hour procedure was similar to that performed Feb. 12 on the left side of Mr. Biden's brain. Under the procedure, a surgeon using a microscope pinches the aneurysm with a clip, bringing the walls of the artery together. The clip remains in the patient.

Mr. Esker said there are no signs of any other aneurysms, adding that the second was much smaller than the first.