Propelled by a small increase in births over deaths and substantial immigration, the American population rose to 245,110,000 as of Jan. 1, 1988, the Census Bureau reports.

The new estimate, the bureau said Tuesday, showed an increase of 2.3 million from 1987 and an increase of 18 million people since the 1980 census.The bureau said the new total, reflecting population growth in calendar year 1987, included "a slight increase" of 1.7 million in "natural growth" - 3.8 million births minus 2.1 million deaths - and a net immigration of 600,000, including 200,000 illegal aliens.

Census Bureau population figures have included the 200,000 illegals as a standard component of its estimates since 1980.

"The absolute number of births in 1987 - 3.8 million - reflects a continuation of the increase in births that have been occurring since the mid-1970s," the report said.

"The increase was initially the result of the large number of `baby boomers' entering their 20s, the prime child-bearing ages," the bureau said. "While not concentrated in the later child-bearing ages, the members of this generation still make up most of the population of potential parents."

The bureau also reported that the nation's black population grew by 1.5 percent in 1987, compared with a growth of 0.7 percent for the white population - although rates of growth have declined substantially for both groups since 1960.

"Fueled by high levels of immigration, the population of other races continued to grow rapidly, increasing by 4.5 percent in 1987."

The proportion of immigrants from Europe has declined from 41.8 percent of the number of all legal alien immigrants in 1964 to 11.5 percent in 1986, the report said.