The Democratic candidates for president, Senators Hillary Rodham Clinton of New York and Barack Obama of Illinois, have championed legislation to reduce such disparities, as have some Republicans, like Senator Thad Cochran of Mississippi.

Peter R. Orszag, director of the Congressional Budget Office, said: “We have heard a lot about growing income inequality. There has been much less attention paid to growing inequality in life expectancy, which is really quite dramatic.”

Life expectancy is the average number of years of life remaining for people who have attained a given age.

While researchers do not agree on an explanation for the widening gap, they have suggested many reasons, including these:

¶Doctors can detect and treat many forms of cancer and heart disease because of advances in medical science and technology. People who are affluent and better educated are more likely to take advantage of these discoveries.

¶Smoking has declined more rapidly among people with greater education and income.

¶Lower-income people are more likely to live in unsafe neighborhoods, to engage in risky or unhealthy behavior and to eat unhealthy food.

¶Lower-income people are less likely to have health insurance, so they are less likely to receive checkups, screenings, diagnostic tests, prescription drugs and other types of care.

Even among people who have insurance, many studies have documented racial disparities.

In a recent report, the Department of Veterans Affairs found that black patients “tend to receive less aggressive medical care than whites” at its hospitals and clinics, in part because doctors provide them with less information and see them as “less appropriate candidates” for some types of surgery.