Americans are living longer than ever largely because of declining death rates from heart disease, cancer and stroke, the federal government said on Monday.

Average life expectancy in the United States rose to a record 77.6 years in 2003 from 77.3 years in 2002, according to the latest data from the Centers for Disease Control and Prevention.

Although women on average still lived longer than men in 2003 - 80.1 years versus 74.8 years - the gender gap in mortality narrowed, continuing a 25-year trend, the CDC said in a report.

The Atlanta-based agency, which is responsible for monitoring and responding to health threats, attributed the improvement in life expectancy to corresponding drops in eight of the 15 leading causes of death.

Chief among them were significant declines in mortality from heart disease, cancer and stroke, the three biggest killers. Death rates for these conditions fell between 2.2 percent and 4.6 percent.

“Those are the big three,” said Donna Hoyert, a CDC statistician and the lead author of the report. “They drive everything else because they’re such large numbers to start off with.”

Lower death rates from HIV, drug and alcohol abuse and use of firearms also helped boost life expectancy.

There were 2,443,930 deaths in 2003, according to the CDC data, which is preliminary. The overall death rate fell 1.7 percent from 2002 when adjusted to account for changes in the age distribution of the population.

The CDC released its data amid rising concerns about a burgeoning obesity epidemic in the nation. Health experts have warned of an inevitable jump in heart disease, diabetes and other diseases if millions of Americans don’t lose weight.

The United States already is struggling with the challenge of caring for an aging population. Death rates from Alzheimer’s and Parkinson’s, two diseases often associated with old age, rose in 2003, the CDC said.

The agency’s data also highlighted continuing racial disparities, with black men on average living 6.2 years less than white men and black women 4.4 years less than white women.