WASHINGTON — Vice President Dick Cheney will have surgery next weekend to repair an aneurysm, a ballooning in an artery, behind his right knee, his office announced yesterday.

The elective procedure will probably be done at George Washington University Hospital, Cheney spokesman Steve Schmidt said. He said the aneurysm was discovered during an annual checkup in July.

The procedure will be performed under local anesthetic and will involve a short hospital stay, Schmidt said.

Unlike aneurysms of the aorta, aneurysms behind the knee do not tend to burst.

But they are dangerous because they can form blood clots that can block blood flow at the knee or travel to the foot and cut off circulation there. Such clots often occur with no warning.

"If they clot off, there's probably a 50 percent chance of losing your leg, whereas if you fix them electively, it becomes a couple of percent," said Dr. Steven Katz, professor of clinical surgery at the University of Southern California's Keck School of Medicine.

Surgery to repair the aneurysm takes two to three hours and can be done several ways. Commonly, the aneurysm is tied off and a vein from the calf or thigh is used to construct a bypass from above the site of the aneurysm to below it.

There are a variety of risk factors for aneurysms behind the knee, which are known as popliteal aneurysms. They include smoking, aging, existing heart disease and family history.

Cheney, 64, has a history of heart problems, dating to 1978, when he suffered the first of four heart attacks. Over the years, he has undergone a series of treatments, including a quadruple bypass in 1988. In June 2001, doctors inserted an implantable cardioverter defibrillator into Cheney's chest to help regulate his heartbeat.

Material from The Washington Post is included in this report.