The death rate from AIDS fell by nearly 50 percent last year, the largest single-year decline for a major cause of death ever recorded, federal health officials reported yesterday.

The huge drop, due largely to the availability of powerful new drug treatments, led AIDS to fall out of the top 10 causes of death in the United States for the first time since 1990. It moved from the 8th to the 14th spot in 1997.

In human terms, the unprecedented decline means that about 16,000 people are alive today who would have died in 1997 had AIDS mortality continued at the previous rate.

Although AIDS mortality has been declining for two years, 1997 was the first full year in which the life-prolonging effects of three-drug antiviral AIDS therapies were felt. The decline in 1997 -- 47 percent -- was nearly double what it had been in 1996.

"It's obviously spectacular," said Donna E. Shalala, secretary of health and human services. "It reflects drug breakthroughs and our ability to get the drugs to people who are infected."

Declining AIDS mortality was just one of numerous pieces of evidence unveiled yesterday of a healthier, longer-living America than has ever existed.

The death rate in the United States as a whole was 478 per 100,000 population last year. This was a record low and represented a decline of 3 percent from the previous year. Hawaii had the lowest death rate, at 375 per 100,000. The District of Columbia had the highest, at 720.

Nationally, an especially dramatic decline in mortality was seen in black men, whose overall death rate fell 7 percent last year. This almost certainly reflected declines in both AIDS and homicide deaths. That one-year decrease nearly matched what had been achieved in the preceding decade -- a 9 percent fall in mortality among black men from 1986 to 1996. The death rate for black women was 4 percent lower in 1997 than in 1996.

An exception to the trend was the 6 percent rise in the death rate of American Indian men last year.

Life expectancy for children born in 1997 was 76.5 years, a record high, up nearly a half-year from 1996. For white women it was 79.8 years (tying a record), and for white men it was 74.3 years. For black women it was 74.7 years, and for black men, 67.3 years. Data for the Hispanic population were not available because of incomplete vital statistics reporting from California.

The national birth rate fell slightly to 14.6 births per 1,000 population, which matched the record low recorded in 1976.

AIDS was not the only major cause of death whose rate declined last year. Heart disease mortality has been declining steadily since 1950; it fell 3 percent last year. Cancer mortality, falling since 1990, dropped another 2 percent. Stroke mortality fell 2 percent. Despite the declines, however, heart disease, cancer and stroke remained the first, second and third leading causes of death in the United States.

Homicide mortality fell 12 percent, suicide 5 percent and accidental death also 5 percent. Mortality from chronic lung disease (mostly emphysema) rose 2 percent, and death from kidney disease rose 5 percent.

The death rates presented in yesterday's report by the National Center for Health Statistics are all "age-adjusted." This is a way of making mortality in the population in one year comparable to that in another year, even though the two populations may have had different percentages of young, middle-aged and elderly people (and, consequently, different actual numbers of deaths from various causes).

About 700,000 Americans are infected with the human immunodeficiency virus (HIV). AIDS deaths peaked in 1995, when 43,115 people died. In 1996, 32,655 people died of AIDS. Last year, the number was 16,685. The age-adjusted rate in 1997 was 5.9 deaths per 100,000 population, compared with 11.1 in 1996.

The only decline in mortality even remotely comparable to that being seen with AIDS was that which occurred with pneumonia after the introduction of antimicrobial drugs, specifically sulfa drugs in the mid-1930s and penicillin in 1941.

From 1929 through 1932, the category of "pneumonia and influenza" was the second leading cause of death, with rates of 147 to 102 deaths per 100,000 population. From 1941 through 1943, it was the fifth leading cause of death, and mortality had fallen to between 67 and 56 deaths per 100,000, according to statistics provided by Robert N. Anderson, a statistician at the National Center for Health Statistics.

Although death from AIDS is declining steeply, the number of new HIV infections each year is essentially stable. There was a 2 percent decline between 1995 and 1996, according to government estimates. In some segments of the population, notably black women and Hispanics, the rate of new HIV infection is on the rise.