WASHINGTON - Women still outlive men, but the gender gap among U.S. seniors is narrowing.

New 2010 census figures, released Thursday, show that men are reducing women's population advantage, primarily in the 65-plus age group. It's a change in the social dynamics of a country in which longevity, widowhood, and health care for seniors have often been seen as issues more important to women.

In all, the numbers highlight a nation that is rapidly aging even as Congress debates cuts in Medicare, an issue with ramifications for the growing ranks of older men as well as women.

Over the last decade, the number of men in the United States rose 9.9 percent, faster than the 9.5 percent growth rate for women. As a result, women outnumbered men by just 5.18 million, compared with 2000, when there were 5.3 million more women than men.

The male-female ratio in the United States also increased to 96.7, from 96.3 in 2000, reflecting the narrowing of the female advantage in overall population. (A score of 100 signifies equal numbers of men and women; a male-female ratio of 95, for example, would mean there are 95 men for every 100 women in the population.)

There has not been such a sustained resurgence in the U.S. male population since 1910, when medical advances started to increase women's life expectancies by reducing deaths during pregnancy.

"I would expect men to become more aware and involved in health care now that they may be affected in the same way as women," said Jen'nan G. Read, an associate professor of sociology and global health at Duke University.

Broken down by subgroups, men were more numerous than women among people 34 and younger, as more boys than girls tend to be born.

At age 35 and higher, the female population historically has been the majority, with men more likely to die prematurely from accidents, homicide, or risks caused by workplace stress, alcohol, smoking, or other factors.

By age 85, the number of women typically is more than twice that of men. Life expectancy at birth is 80.8 years on average for women, compared with 75.6 for men.

But over the last decade, the gender gap narrowed. Since 2000, the number of men 65 and older increased by 21 percent, compared with 11.2 percent growth for women in that age group. Among people 65 to 74, the male-female ratio also narrowed sharply. Women in that age group outnumber men by roughly 1.5 million, down from 1.8 million in 2000.

The latest census figures come amid a graying baby- boomer demographic of 78 million people - now ages 46 to 65 and looking ahead to retirement - who will have a major voice in the 2012 elections as federal spending and the spiraling costs of Medicare rise to the forefront.

Last month, the Republican-controlled House approved sweeping changes to Medicare for people younger than 55, but the party has begun to pull back after meeting stiff protests from older voters.