The Loudoun County School Board last week voted to delay $1.8 million worth of building projects planned for this school year.

The capital improvement cuts are expected to be only the first -- and perhaps the easiest -- in the board's efforts to balance the budget at a time when the county expects a shortfall of up to $34 million next year.

By putting off school additions, laboratory improvements and new tennis courts, the board hopes to save a total of $5.1 million during the next five years, school officials said.

Superintendent David N. Thomas has estimated that the 14,500-student system will need at least $11 million more from the county next year to maintain existing programs. Thomas said he expects losses of at least $4 million in state aid.

The capital improvement fund is separate from the school operating fund, but it comes from the same pool of money the county has to spend, said board member Barbara B. D'Elia (Dulles). D'Elia and other school officials hope that by cutting capital expenses, they will have more money for operating expenses.

"That's why we took a very hard look and made some significant cuts," she said of the capital improvement project delays, announced at the School Board meeting last week. "The toughest road is yet to come."

Frederick F. Flemming (Leesburg), who called for a time of austere spending at the board's meeting, said the board made the cuts at the request of the Board of Supervisors. In September, the supervisors asked for cutbacks after taking the unusual step of predicting a shortfall of $28 million to $34 million for next year.

"They asked us to defer or eliminate," Flemming said. The School Board will begin focusing more on where to cut the operating budget, which includes academic program expenses, salaries and other day-to-day matters.

The Board of Supervisors met with the School Board last Thursday. Officials said the supervisors appreciated the savings, but may ask for more cuts or project delays. "That's a possibility," said John Wells, director of the county Office of Management and Budget.

According to Edgar Hatrick, the assistant superintendent for planning and pupil services, project delays include: Improvements at Guilford Elementary School that were expected to cost $226,000. The project has been delayed for at least two years. New tennis courts at Loudoun Valley High School, for savings of $208,000. The project has been put off until the 1991-92 school year. Additions to the Monroe Vocational Technical Center, for a savings of $360,000.

Hatrick said more money would be saved in the short run by a plan to upgrade four middle school science labs instead of following through on extensive laboratory improvements the board had approved earlier.

He said any project that is delayed would cost more to complete later because of inflation. Construction of a new Broad Run High School, at a cost of $34 million, will continue as planned, he said.