Results of the triennial school census released last week showing a dramatic decline in the number of children of pre-school age are being studied by Arlington County school officials.

According to the census, the number of children ages 1 to 4 in Arlington County has decreased by 40 per cent since 1974, when the last census was conducted. State revenue allocations are based on the census results. School superintendent Larry Cuban said he did not yet know what effect the results would have on Arlington's allocation.

"The census results indicate that enrollment looks like it will continue to decline. We had hoped it would bottom out," Cuban said.

According to school officials, the 1977 census also reveals that:

There has been a decline of 15.6 per cent in the 1-19 age group since 1974

Public school enrollment has increased by six per cent since 1971.

The latter finding, coupled with a school board-sponsored study that shows declining private school enrollments, seems to conclusively refute charges made in the recent county board race. Unsuccessful candidates Arthur C. Vogel and Sherman W. Pratt repeatedly charged that steadily declining enrollment figures were indicative of dwindling public confidence in the school system.

Incumbent board member Ellen M. Bozman, whose campaign platform included strong support for the county's school system, won re-election by a decisive margin. School officials said that they consider the development a heartening affirmation of the school board's policies and actions.

School officials say that unless the demographic trend is reversed, more schools will probably be considered for closing in the next few years. The school board's decision to close Stratford and Gunston Junior High Schools effective at the end of this year has sparked protests by some parents who regard the closings as unnecessary and ill-advised.

"We review our policy on closing each year," said school board chairman Dr. Thomas Penn. He said he was surprised at the extent of the population decline reflected in the census figures. "But there's no straight line correlation," Penn said, nothing that declining enrollment is only one of several factors the board weighs in making closure decisions.