WASHINGTON — New government research has found "large and growing" disparities in life expectancy for richer and poorer Americans, paralleling the growth of income inequality in the last two decades.

Life expectancy for the nation as a whole has increased, the researchers said, but affluent people have experienced greater gains, and this, in turn, has caused a widening gap.

One of the researchers, Gopal K. Singh, a demographer at the Department of Health and Human Services, said "the growing inequalities in life expectancy" mirrored trends in infant mortality and in death from heart disease and certain cancers.

Singh said last week that federal officials had found "widening socioeconomic inequalities in life expectancy" at birth and at every age level.

He and another researcher, Mohammad Siahpush, a professor at the University of Nebraska Medical Center in Omaha, developed an index to measure social and economic conditions in every county, using census data on education, income, poverty, housing and other factors. Counties were then classified into 10 groups of equal population size.

In 1980-82, Singh said, people in the most affluent group could expect to live 2.8 years longer than people in the most deprived group (75.8 versus 73 years). By 1998-2000, the difference in life expectancy had increased to 4.5 years (79.2 versus 74.7 years), and it continues to grow, he said.

After 20 years, the lowest socioeconomic group lagged further behind the most affluent, Singh said, noting that "life expectancy was higher for the most affluent in 1980 than for the most deprived group in 2000."

"If you look at the extremes in 2000," Singh said, "men in the most deprived counties had 10 years' shorter life expectancy than women in the most affluent counties (71.5 years versus 81.3 years)." The difference between poor black men and affluent white women was more than 14 years (66.9 years vs. 81.1 years).

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

• People who are affluent and better educated are more likely to take advantage of new discoveries to detect and treat many forms of cancer and heart disease.

• 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 unhealthful 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.

A recent study by Ellen R. Meara, a health economist at Harvard Medical School, found that in the 1980s and 1990s, "virtually all gains in life expectancy occurred among highly educated groups."