Future demographic trends, including possible racial makeup of neighborhoods in the eastern sections of Prince William County, were a factor behind the high school boundary change recommended by the school administration and adopted last week in a 4-to-3 vote by the School Board, school officials have said.

The boundary change, approved by the board after a month and a half of acrimonious debate, will send neighborhoods just west and south of Lake Ridge to Gar-Field High School. Sections of Woodbridge along Rte. 1 will remain in the high school that bears their community's name.

The new boundaries are based on elaborate population projections by school officials. The new boundaries for Woodbridge High School will incorporate areas projected as stable in population, meaning that enrollments at the school are unlikely to grow beyond a "worst-case" peak population of 2,940 students in 1991. Then the population will decline, according to schools planner Charles McLeod.

"I feel confident that we're not going to be proved wrong," said McLeod, who has served as the administration's point man on the redistricting debate. McLeod's crystal ball also shows Gar-Field with room to grow in 1991, with about 2,520 students. Planners project rapid growth in Westridge.

While school officials have steadfastly maintained that present socioeconomic balance between the two schools was not a factor in the boundary recommendation, future racial trends were considered, according to Superintendent Edward L. Kelly, although he emphasized that they were not the prime consideration.

Gar-Field's black enrollment is 18 percent. Woodbridge's is 8 percent, and the county school average is 11 percent. Gar-Field now draws almost entirely from eastern and northern sections of Dale City, where housing is moderately priced by county standards.

By incorporating into Gar-Field areas west of Lake Ridge where substantial growth is likely and where housing is relatively expensive, Kelly said the system avoids having an "enclosed" area going to one school. Lake Ridge, while racially integrated, is predominantly white, and population growth west of that area is expected to continue that trend.

Kelly, who came from Little Rock, Ark., where matters of racial balance in the schools consumed much of his time, said his experience there sensitized him to the issue. "There is no doubt that an experience like that makes you more sensitive," he said. "You don't want to get yourself in the position where racial balance becomes a problem."

Although "hard data" on county racial trends is scarce, Kelly added, "We are all aware of the issue. It is our responsibility to avoid the district getting involved in some of those issues. We don't even want to take a risk."

Conflicting definitions of "neighborhood school" punctuated the debate before last week's vote.

Citizens in areas adjacent to Lake Ridge, where Woodbridge High School is located, urged the board to consider only geography.

"Woodbridge High School is a neighborhood school for Lake Ridge, not for Woodbridge," one father proclaimed at a public hearing.

But residents of the old neighborhoods of Woodbridge along Rte. 1 argued for tradition as a criterion for the new boundaries.

"People in my district have worked hard, paid taxes and supported that school {Woodbridge High} for 15 years. It's not right to see that thrown down the drain," said School Board Chairman Gerard P. Cleary (Woodbridge).

Other boundary change options before the board would have sent one or both of those neighborhoods from Woodbridge to Gar-Field.

Many observers concluded that politics played a part in the board's decision, a charge hotly denied by those who supported the boundary.

For instance, the new boundaries, which will split the Occoquan District between two high schools, have been interpreted by some as a slap against Board of County Supervisors Chairman Kathleen D. Seefeldt (D-Occoquan). Seefeldt made clear in January that the School Board's request to go to the state for Public School Authority bonds stood no chance of approval by the board.

Woodmont, Seefeldt's neighborhood, will be transferred from Woodbridge to Gar-Field High School, as will Rollingwood Village and other nearby subdivisions in her district.

Donna Blanton, chairman of a committee that helped pass a $44.89 million school bond in November and will spearhead the next bond drive, said polarization over school boundaries concerns her. "Any boundary change is bound to have an impact," she said.

The following areas are being moved from Woodbridge High School District to Gar-Field High School District: Woodmont; Forest Vista; Elm Farm Mobile Homes; Dale View Manor; Rollingwood Village; Longwood Estates; Hunter Hills; Twin Oaks Farm; Omisol Road; Gleatons Mobile Homes.