Nearly 183 million Americans will be old enough to vote in the presidential election this year, about 8.1 million more than in 1984, the Census Bureau has estimated. But if tradition holds, only about half the eligible voters -- people age 18 or over -- will cast ballots.

The 1984 turnout was only 53.1 percent of the voting-age population, up from 52.6 percent in 1980. The record turnout was in 1960, when 62.8 percent of the voting-age population participated.

Of the 182.6 million Americans old enough to vote, the bureau estimates that 52 percent are women. Eleven percent are black and 7 percent are Hispanic.

The bureau study found that the voting-age population continues to be concentrated in the baby-boom group. People age 25 to 44 will total 79.4 million by Election Day 1988, or 43.5 percent of all Americans of voting age.

Americans age 65 or over, who have a high voting rate, have increased by 5.1 million since 1980 to a total of 30.6 million or 16.8 percent of eligible voters. But the youngest group of voters, age 18 to 24, has declined to about 26.5 million, or 14.5 percent of the total. Middle-age voters, in the 45-to-64 age group, are 25.2 percent of the total.

Overall, nearly one voter in three lives in the South, the report said.