Vice President Cheney is scheduled to have surgery today to repair an aneurysm in his right knee and then have a similar operation later on an aneurysm behind his left knee.

Cheney is expected to remain at George Washington University Hospital for as much as 48 hours after the surgery, said Lea Anne McBride, spokeswoman for the vice president. The aneurysms, known as popliteal aneurysms, are not considered life-threatening, and doctors say the surgery is minimally invasive.

"It's not complicated if you're experienced," said Peter Kalman, professor of surgery and radiology at Loyola University Chicago Stritch School of Medicine.

The surgery is to be performed under local anesthetic, Cheney's office said. The condition was discovered during Cheney's annual physical in July. An aneurysm is a ballooning weak spot in an artery that, as blood pounds through, can burst if left untreated.

Cheney's aneurysm is expected to be treated with a stent graft threaded through a catheter inserted in the femoral artery at the groin down to the aneurysm site. Fully opened, it is like a little tube inside the artery, keeping the blood from touching the weakened artery walls. This is a newer technique for patching aneurysms, and an alternative to rerouting blood flow around the weak spot with a vein bypass.

"This is an unconventional approach . . . although it's becoming something that most of us are doing in our practice," said Thomas Bernik, chief of endovascular surgery at St. Vincents Hospital and Medical Center in Manhattan. He said that if the aneurysm was directly behind the knee, "you do not have a very good result long-term-wise" with a stent. He said that was because the knee is constantly bending, and the stent can break or crack.

However, he said Cheney might not have a vein available for a bypass. Kalman said the long-term durability of the stent approach was not known. But he said it was less traumatic and less painful and involves a shorter hospital stay.

Cheney, 64, has had four heart attacks, though none since he became vice president in 2001. That year, he had an implantable cardioverter defibrillator inserted in his chest. The pacemaker starts automatically if needed to regulate his heartbeat.

A vascular exam, part of a two-part annual physical Cheney completed in July, identified "small, dilated segments of the arteries behind both knees." But his overall cardio health was judged to be good after the first part of the exam, which included a general physical exam, an electrocardiogram and a stress test.

The checkup determined that the pacemaker was working well and had never had to be activated.