Supreme Court Justice Ruth Bader Ginsburg, 66, underwent surgery for colon cancer yesterday at Washington Hospital Center. It was not known late yesterday how long her recuperation would take or when she would be able to return to the high court, which begins its new term Oct. 4.

In a statement released by the court, Ginsburg's surgeon, Lee Smith, said the justice likely will remain in the hospital for a week.

Ginsburg, who was appointed in 1993 by President Clinton and is the second woman on the court, became ill while in Crete this summer, teaching in a Tulane Law School program. Her condition initially was diagnosed as acute diverticulitis, and she was treated until last week for that gastric disorder. Last week, however, tests at Washington Hospital Center diagnosed her illness as cancer, court spokeswoman Kathy Arberg said.

Colon cancer is the third most common cancer in the United States in annual deaths and new cases each year. Nearly three-quarters of all cases occur in people aged 65 or older. Both incidence and mortality are higher in men than in women.

As with many cancers, survival depends highly on the stage of the disease at the time of diagnosis.

About 90 percent of people survive at least five years when the tumor is confined to the colon. Slightly more than one-third of cancers are found at this stage. If the tumor has spread to surrounding tissue, about 66 percent of people survive five years. Survival falls to about 9 percent if it has spread to distant organs, such as the liver.

Surgery is the initial treatment in all three stages. Often, chemotherapy is given afterward. In widely disseminated disease, chemotherapy's purpose is to slow growth of the cancer rather than cure it.

Initially, colon cancer sometimes masquerades as diverticulitis, which is an inflammation of the wall of the colon that often causes abdominal cramping and pain.

Smith did not speculate as to when Ginsburg will return to full-time activities at the court, according to Arberg.

Absence from the court for health reasons has not disqualified missing justices from voting on cases even if they have not heard oral arguments. However, if the justice has not participated at all in the case, only the remaining eight justices would vote.

Clinton said he chose Ginsburg, his first appointee to the court, for her moderate judicial approach and her legendary role in fighting for equal rights for women. (Clinton's other appointee was Stephen G. Breyer, in 1994.) Ginsburg also was the first justice appointed by a Democratic president in 26 years, since President Lyndon B. Johnson named Thurgood Marshall in 1967. Ginsburg, a native of Brooklyn, also became the court's first Jewish member since the resignation of Abe Fortas in 1969.

Ginsburg was a judge on the U.S. Court of Appeals for the D.C. Circuit from 1980 to 1993. She gained a national reputation in the 1970s as a women's rights advocate, devising a legal strategy that secured constitutional protection against sex discrimination. On the high court, she has remained vigilant in her concern for women's rights. Overall, she is a cautious liberal and has become most aligned with Breyer and David H. Souter, who was appointed by President George Bush in 1990.

Cancer has had a profound impact on Ginsburg's life. Her mother, Celia Bader, died of cervical cancer the night before young Ruth was to graduate from high school in 1948. Then, a few years after she married Martin Ginsburg in 1954 and while he was still in law school, her husband was diagnosed with testicular cancer. Martin Ginsburg recovered and is a prominent tax lawyer and law professor. They have a grown son and daughter.

Ginsburg keeps an active speaking and lecturing schedule, usually taking at least one trip abroad during the court's summer recess.