HOW MANY Hispanics are there in the United States? A lot more today than in 1980, the Census Bureau reports, although it admits it doesn't have the precise answer because it has been changing its definition of "Hispanic," first in the 1980 Census, then in estimates it has just released for 1986 and 1987. The changes were made for good reasons and have had the effect of spreading a wider net and increasing the number of residents classified as Hispanic; the latest figures even take into account the illegal migrants of the 1980s.

Even discounting for these changes in definition, it's clear that the Hispanic population is growing rapidly. The numbers were 9.4 million in 1970, 14.6 million in 1980, and 18.8 million in 1987. Just 4 1/2 percent of Americans were counted as Hispanic in 1970, compared with 6 percent in 1980 and 8 percent -- about one out of 12 Americans -- in 1987.

Of course, Hispanics are not a single homogeneous group, any more than the European immigrants of 1880-1924 were. Cuban-Americans, concentrated in the Miami area and a few eastern cities, have relatively high education and income levels; their numbers stopped increasing in the middle-1980s. Central and South Americans are increasing rapidly in numbers; their socioeconomic status is much lower. Mexican-Americans are by far the most numerous group, accounting for 5 out of 8 Hispanics; but that leaves 3 out of 8 -- some 7 million Americans -- in other groups.

Overall, Hispanics in the United States have relatively low education levels; only a bare majority have four years of high school. But their incomes have increased, and their poverty level has decreased since the 1981-82 recession, despite the arrival of hundreds of thousands of newcomers. Unemployment among Hispanics is not vastly higher (9.5 percent in March 1987) than among non-Hispanics (7 percent); families are larger and only a bit less likely to be headed by a married couple. Family incomes of Hispanics have risen in pace with those of other Americans but are still about one-third lower; about one-quarter of Hispanics live below the poverty line.

One way of looking at these numbers is to say that Hispanics tend to be behind other Americans, to suffer from disadvantages; another is to say that they are moving up rapidly, especially when you consider that many started off living elsewhere, in circumstances you will not find statistically replicated anywhere in the United States. Hispanics are moving up the many ladders of success in America. The numbers show a country increasingly Hispanic, but they only begin to suggest the drama of personal struggle and achievement which lies underneath them.