Enrollment in the District of Columbia public schools declined by about 8,000 students between September 1977 and September 1978, the biggest drop in a pattern of falling enrollments that began a decade ago.

School officials and outside analysts attribute the decrease to the nation's over-all declining birth rate and the shift of black families from the city to the suburbs, among other factors.

Although suburban school enrollments have also fallen, Prince George's County schools have absorbed nearly 4,000 students this fall who attended D.C. schools last year. Prince George's is the only suburban Washington school district that keeps track of the number of D.C. students transferring into its schools.

"There is an exodus of black families from the District to P.G. County and to some extent the other counties, Montgomery and Fairfax," said George W. Grier, a specialist in demographics and housing patterns in Washington. "It is almost the same as the exodus of white families from the District that took place a decade ago."

District schools have not yet released statistics on the racial composition of the school system, but enrollment figures for individual schools indicate that schools in the mostly white area of the city west of Rock Creek Park had increases in enrollment. In 10 schools in that area the number of students rose slightly.

At the same time, the number of students decreased in mostly black schools in areas of the city that are undergoing massive renovation, Du-Pont Circle, Capitol Hill, Adams-Morgan, and new Southwest.

Still, it is not clear from the enrollment statistics that the students entering Prince George's County schools are the same students leaving some D.C. neighborhoods because of widescale renovation and rising rents.

"Now you have blacks moving to the suburbs for better schools, too," said Grier. "Middle-class and affluent blacks who want the best for their kids. In the past those blacks didn't move out of the city because of discrimination and the cost of housing.Now they can afford it and more are making the move . . . "

The city school system now has its lowest enrollment since 1957, and lost 37,584 students since the peak enrollment of 1969.

The D.C. schools had 111,532 enrolled students as of September.

School officials had anticipated a loss of about 4,000 students based on a continuation of the steady decline since the late 1960s, when the children of the post-war "baby-boom," began to rise above school age.

But the almost 7 percent plunge in enrollment for the D.C. system, twice what school officials had projected in their budget proposals for Congress, was the steepest ever. The schools lost students on both ends of the spectrum. The number of high school students dropped for the second time and the number of prekindergarteners also went down.

School officials had expected the number of prekindergarteners to increase because the school board made prekindergarten classes available to every child in the city this year for the first time.

School Board member Betty Ann Kane (at-large) who chairs the committee on school finance, said the drop in prekindergarten enrollment was due to cutting the school day from a full to a half day.

" . . . In order to make available the prekindergarten classes to everyone, the board had to go to half-day classes," she said, "and that is not as attractive or useful to working parents . . . "

One school official sees no connection between declining enrollment and falling nationwide birth rates.

"What no one talks about," said Frank Shaffer-Corona, at-large member of the school board, "is that the end of the baby boom does not affect the minority community. The birth rate among blacks and Latinos is such that we are not having fewer children . . . We don't have a decrease in the number of children who need an education. We have an increase in dropouts, uneducated people who are pushed out of the community through displacement as the whites come in . . . "

School board president Conrad Smith cites an increase in the number of private schools here and "a disproportionate number of white parents who send their children to private schools."

"Another factor," Smith added, "is that rightly or wrongly there is widespread feeling of dissatisfaction with the public schools among white, black and Spanish parents. They feel the public schools are not delivering the kind of education they want for their children."

In recent years school officials have had to argue their need for bigger budgets to improve school facilities and programs despite lower enrollments.

William Spaulding (D-Ward 5), chairman of the City Council's Education Committee, predicted that the drop in school enrollment will not lead to budget reductions for several years. The school system's $264 million budget for fiscal 1980 is $11 million more than the fiscal 1979 budget but $16.2 million less than the school board had requested.

"Facility costs are going up and personnel costs are going up," Spaulding said, "and they are both going up faster than enrollment is coming down . . . and you have to remember there was a time when the budget was grossly inadequate."

But Sam Starobin, director of the D.C. Department of General Services, believes the fall-off in enrollment may justify a reduction in the school budget, particularly in money allocated for construction and renovation.

Starobin questioned whether the school board had fully considered enrollment trends in its $30 million to $40 million renovation program. "It could be one hell of a waste of money," said Starobin. " . . . The last high school they built, Dunbar, was intended to hold 2,000 and now it has about 1,400."

Several D.C. schools are operating below capacity - including Bunker Hill Elmentary at 55 percent of capacity, Lincoln Junior High at 59 percent, and Randall Senior High at 32 percent. But over the last five years, the school system has built 20 new schools and several annexes to existing schools in its biggest building program ever.

A 1977 report by the General Accounting Office calculated that the school system had 19,000 excess seats and would have a surplus of 28,000 seats by 1980.

In March of this year, Superintendent Vincent E. Reed asked the school board to close 23 schools, but vehement protests in several neighborhoods kept 14 of those schools open.