FOR DECADES, the Census Bureau has been compiling data on public and private school attendance. These figures have, of course, been published, but always as part of a larger compilation of statistics. Last week, the bureau released a report that pulled together all these school attendance figures and, in the process, destroyed the myth that private schools have been growing at an enormous rate at the expense of the public schools. Statistics show that this is simply not true.

At the end of the '50s, 14.4 percent of elementary school children and 11.1 percent of high school students were enrolled in private schools. During the next two decades, school enrollment in general fell off because of a decline in the birthrate. But in that same 20-year period, public schools increased their share of enrollment while private schools experienced dramatic losses. By the school year 1979-80, only 11.2 percent of younger children and 7.4 percent of teen-agers were enrolled in private schools, most of them in the northeastern and north-central states.

Why are a greater percentage of Americans sending their children to public schools today than did so 20 years ago? One reason may be the increased funding and better facilities and programs that came with federal aid. The last two decades saw massive infusions of assistance from Washington, which enabled public institutions to offer many of the special advantages that had been available only at great cost in the private system. Another reason is the decline of Catholic school enrollment. More Catholics have moved from the central city to the suburbs, and it has been suggested that parochial schools were not as readily available there. Others lost the desire for ethnic and religious separation, which had been more prevalent before Vatican II. And, as our society has grown more heterogeneous and tolerant, many Catholics have felt more comfortable in public schools than they had been in earlier days when they were a distinct minority.

These figures may also tell us something encouraging about school integration. First, we have not seen a massive turn away from the public schools since integration. In fact, private school enrollment peaked at 15.4 percent in 1964, the very year the federal government began a concerted effort to guarantee integrated schools, and continued to fall throughout the '60s and '70s at a time when courts were ordering wide-scale busing. True, during this period private school enrollment rose very slightly in the South -- the only area in the country where this occurred -- but in a national school population of 38.8 million, these figures are not especially significant.

Where white flight did occur in cities outside the South, dramatic losses in the first year of busing were most often reversed in later years. The study also reveals that while the public schools were being integrated, so were the private schools. Many made an effort to recruit minority students. Black families became more able to afford private school tuitions. The result is that while overall enrollment in private schools has fallen, the percentage of blacks in these schools has more than doubled.

All this information on increased enrollment, combined with the good news about rising test scores, creates a picture of a healthy and improving public school system -- in case you were looking for some good news.