New government figures on Americans' average life expectancy, calculated for infants born in 1988, show a widening gap in life expectancy between whites and blacks, with white Americans living more than six years longer. But preliminary figures for babies born in 1989 suggest that black life expectancy may be starting to catch up.

The figures indicate that the average difference in lifespan between whites and blacks is now narrowing, after a four-year interval between 1984 and 1988 when it grew from 5.6 years to 6.4 years.

The final 1988 figures, released this week, show that for blacks, average life expectancy was 69.2 years, and for whites, 75.6 years. But provisional 1989 figures show the gap narrowing to 6.2 years. Black infants born in 1989 had an average life expectancy of 69.7 years, and white infants, 75.9 years.

Last year also marked a distinct improvement for the population as a whole over 1988, when an unusually severe outbreak of influenza caused average life expectancy to fall for the first time since 1985.

No data were released showing how life expectancy differed by income as opposed to race.

The 1989 increase in blacks' life expectancy came despite a 32 percent increase in U.S. deaths from HIV infection over 1988, as AIDS jumped from the 15th to 11th leading cause of death. Homicide also advanced from the 11th to the 10th major cause of death in 1989, with 9.3 deaths per 100,000.

The death rates for six major diseases, however, were lower in 1989 than 1988: cerebrovascular diseases, diseases of the heart, accidents, pneumonia and influenza, atherosclerosis, and septicemia (blood poisoning).

In the final statistics for 1988, released this week, heart disease, stroke and cancer all showed a decline from the preceding year as causes of mortality.

"As we succeed in reducing mortality from the leading causes of death, we must address the increasing risk from homicide and HIV infection," Centers for Disease Control Director William L. Roper said. "I am convinced that the health education and prevention efforts, which served so well in combating chronic disease, can also be effective in helping us deal with these new threats."

Overall life expectancy for females in 1989 was 78.3 and for men, 71.5. The difference in male and female life expectancy, which had widened considerably between 1900 and 1972, has narrowed since 1979.

For black women and men, life expectancy was 74 and 65.2 years respectively, while for white women and men it was 79.1 and 72.6 years, respectively.

The infant mortality rate for 1989 was 973.3 deaths per 100,000, 2 percent lower than 1988 and the lowest U.S. rate ever recorded. This eclipses the record low set in 1988, when the rate dropped 1 percent over the previous year. However, the rates of decline in infant mortality have been slowing since the late 1970s, and there continue to be large differences in mortality of blacks and whites.

"These numbers lose their impact when black babies continue to die at a rate twice that of white infants and thousands of babies continue to be born at low, life-debilitating birthweight," said Rae Grad, executive director of the National Commission to Prevent Infant Mortality.