ARLINGTON — Facing a possible $2.4 million budget shortfall, School Board members recently took the first swing in what will likely be a hard-fought battle with their 2010-11 budget.

The Board unanimously approved an enrollment projection for next school year during its Feb. 8 meeting, agreeing that an average of 5,100 full-time equivalent students will be enrolled in Arlington schools.

After much deliberation, Board members settled on the conservative end of Superintendent Kristine McDuffy’s recommended range of 5,100-5,140 full-time equivalent students.

McDuffy and other department administrators analyzed multiple data sources and enrollment numbers during their recommendation, according to a school district memo. Much of that information was shared with the Board during its Jan. 8 work session and its Jan. 22 Board meeting.

“We’re not thinking about the start of (next) year, but for the average amount during the year,” said Deb Borgens, district executive director of financial services.

School districts receive funding based on their enrollment numbers.

During recent years the school district has seen shrinking enrollment in its schools which culminated in a number of layoffs and budget reductions before the 2009-10 school year.

But Borgens said that so far enrollment within the school district this school year has remained relatively steady with last year’s Board projection, which was also 5,100 full-time equivalent students.

“That’s encouraging that we don’t have as many people leaving our community,” Borgens said, adding that the recent announcement of Walmart coming to Arlington could be a benefit to the community.

Board members initially wanted to be more conservative with their enrollment projection than McDuffy’s recommendation.

Board member Jim Weiss said he thought 5,000 students would be a better estimate for next school year. He asked Borgens how much of a difference 100 students could make in the budgeting process.

Borgens said that 87 percent of the district’s budget is compensation for employees, and guessed that removing 100 students from the Board’s estimate could mean $600,000-$800,000 — or up to 20 jobs — could be lost.

“It would be a deeper rift,” Borgens said.

Board member Kay Duskin said that she would feel more comfortable with a 5,050 enrollment estimate, while Board member Bob McClure voiced his support for McDuffy’s 5,100 recommendation.

“I don’t want to outguess the work that’s gone into this,” McClure said.