The Arlington School Board last night began what is expected to be a lengthy process of reexamining racial balance in a school system that has changed dramatically since the last all-black county school was desegregated 15 years ago.

Board members said they will vote at their May 8 meeting on recommendations from Superintendent Arthur W. Gosling to honor a request from some black parents for a change in a school attendance policy and to prepare a fall report on the racial balance issue.

While blacks once composed the only significant minority in the county's schools, today about 16.2 percent of the system's 14,500 students are black, compared with 14.5 percent Asian and 14.7 percent Hispanic enrollment.

The issue arose last month when parents of 15 black students who are now third graders at Barcroft Elementary School asked that their children be allowed to stay there through the sixth grade instead of being bused to other schools for the fourth, fifth and sixth grades.

The children are all from the predominantly black Nauck area in South Arlington once served by Drew Elementary School. That school was closed as an ordinary grade school in 1971 as part of a court-approved School Board plan to desegrate Drew, then the only remaining all-black school in the county.

Drew reopened as a "model" grade school with specialized curriculum that was to draw about 11 percent of its enrollment from the immediate black neighborhood.

But the plan was bitterly opposed by black parents and some whites who sued the School Board in U.S. District Court in Alexandria, contending that the burden of desegregation was placed solely on black students who were to be bused to predominantly white grade schools throughout the county.

The plan called for those black students to enter their grade schools' normal "feeder" intermediate and high schools. The federal court upheld the plan, which the School Board at the time said would result in black enrollments of 7 to 15 percent at all schools.

The court did not set a specific minimum percentage for black enrollment.

Three years ago, however, the School Board granted the request of Nauck parents who asked that children in the first three grades who were being bused to the four northernmost schools be allowed to attend schools closer to their South Arlington homes. The parents complained that busing such young children disrupted their lives. Children in grades four through six, however, were to continue being bused to the northern schools.

Last year, the School Board agreed to let the black students in the third grade stay through the fourth. A few weeks ago, parents of 15 black third graders at Barcroft asked that they be able to complete their grade school educations there, citing the disruption of being moved from one school to another.

Gosling is recommending that the requests be approved, but he also cautioned that it could lead to pressure to let those students continue with their classmates to intermediate school and high school -- a proposition that could alter racial balance in those schools. He also warned that it could result in similar requests from black parents whose children also split their grade school educations at other schools.