The number of black students attending Washington's public schools declined last fall by 6 percent, the sharpest drop ever, while the small number of whites also fell, despite a reported rise in the city's white population.

Blacks account for 94.6 percent of the District's public school enrollment, according to the official fall enrollment report. This is the highest proportion of blacks in any large school system in the United States, although it is slightly less than the peak of 95.7 percent reached here in 1973.

Officials have suggested that the decrease in black students -- the number is down 6,836 from a year ago -- reflects the continued movement of black families to the suburbs as well as a decline in births and the virtual end of migration from the South.

The major exodus of white families from Washington occurred in the 1950s and 1960s. According to District of Columbia government estimates, the white population rose by almost 10,000 from 1975 to 1977, but demographers say most of the newcomers are single adults or childless couples.

In addition, according to 1977 figures, about 60 percent of the city's white children attend private schools. The number of D.C. whites in these schools rose by 771 from 1975 to 1977. During the same two years the number of whites in public schools fell by 17. For fall 1978 the drop in white public school enrollment was 206.

"Over the past 10 years the public schools have become the place for people who can't afford to put their children in private schools," said Minnie S. Woodson, the new president of the D.C. Board of Education. "Or parents send their children if they feel they (the children) are strong enough to take it. I think it's sad in a way but that's what has happened to the public schools."

But Woodson added: "I think in the next three years we have a very good chance of getting a turnaround..." Woodson said she based her optimism on the gradual implementation over the next several years of Competency Based Curriculum, or CBC, throughout the school system.

According to the enrollment count taken on Cot. 19, there are 106,977 black students in the Washington school system this school year out of a total enrollment of 113,050. The number of whites is 4,216 or 3.7 percent of the total.

In addition, the school system has 1,165 Hispanic students, 656 Asians, and 36 American Indians. The Hispanics account for 1 percent of citywide enrollment, but they are the only group to have increased steadily since 1975, when they numbered just 887.

The overall enrollment decline of 6,915, compared to October 1977, was the largest one-year drop the school system has ever had, although the decline was about 1,000 less than reported earlier, based on September figures. Officials said the September to October change reflects an influx of late entrants, particularly among kindergarten children and those in high school who had dropped out but then decided to return.

According to the report, the loss of black students has occurred in all sections of the city including Anacostia, where growth was most rapid in the 1960s and continued until 1975.

But the sharpest drop was in older in-town areas -- including Adams-Morgan and the fringes of Capitol Hill -- where houses are being renovated and black families, usually low-income renters, are being replaced by whites. The smallest declines were in upper Northeast Washington and upper Northwest east of Rock Creek Park, where black homeowners predominate.

At the Marie Reed Community School in Adams-Morgan, for example, black enrollment in elementary grades dropped by 107 students last fall to 468, while at nearby Adams School the figure dropped by 48 students to 250. There were only 16 whites at the two schools, seven fewer than in the previous year.

In schools close to the U.S. Capitol, black enrollment was continuing to decline, but the number of whites also dropped slightly last fall, apparently because of the expansion of private schools in the neighborhood.

The enrollment report indicates that white students are heavily concentrated west of Rock Creek Park, the only large area of the city that is predominantly white.

Throughout the rest of the city 140 public schools are at least 99 percent black, most of them with no whites at all. But west of the park eight elementary schools have white majorities, which generally are holding steady, including three schools that are slightly more than 80 percent white.

The Hardy Middle School on Foxhall Road NW, which enrolls youngsters in grades five to eight has a slight white majority. Among its students is President Carter's daughter Amy, who transferred into the school in September.

This year 54 percent of Hardy's 204 students are white, 24 percent black, 19 percent Hispanic, and 3 percent Asian. In the sixth grade, in which Amy Carter is enrolled, about three-quarters of the children are white.

Last year Amy attended the public school closest to the White House, Stevens Elementary at 21st and K streets, NW, which was 17 percent white. The number of whites enrolled at Stevens dropped to 20 last fall from 43 a year earlier. The number of blacks has fallen too, though not so abruptly, as the school has stopped accepting new students who live outside its attendance area.

None of Washington's 47 junior and senior high schools have white majorities. Even at Deal Junior High and Wilson High School, both in a white area near Tenley Circle, the proportion of white students is relatively small -- 36 percent at Deal and 21 percent at Wilson. This fall the number of whites at both schools declined slightly.

In elementary schools whites make up 4.9 percent of citywide enrollment, in junior highs, 2.5 percent, and in senior highs just 2 percent, the report indicated.

According to city government estimates, Washington's overall population was 75 percent black last year.

Black school enrollment peaked in 1969 at 140,667 and has dropped 24 percent since then.