Two development proposals that could triple the population of Haymarket are causing some town officials to rejoice and giving Prince William County school authorities a headache.

The proposals, which will be considered by the town council early next year, would bring 170 town houses to the one square mile town of 325 residents. If a second developer can persuade town officials to change the zoning ordinance, 64 apartments could also be added to those numbers.

The zoning ordinance currently allows only single family dwellings. Two public hearings, one to be held by the planning commission and the other by the town council, are required before such a change can be made.

According to planning commission chairman Dennis Wrye, the town houses will be a welcome addition to Haymarket. "The great majority of our residents are renters," said Wrye. "Having homeowners here who have a vested interest in the town can only help us." The apartments will not be so welcome, he said. "They'll only bring in more renters."

Charles Wildman, supervisor of programs and planning for the Prince William County schools, said school officials are watching development in the western end of the county, particularly in the Haymarket-Gainesville area, with growing concern. When the school staff prepared its five-year housing projections earlier this year, the Haymarket developments were not part of the picture. According to Wildman, the two elementary schools just outside Haymarket, Tyler and Gainesville, are near capacity now.

Gainesville, which has second through fifth grades, has a 275-student capacity. Wildman projects that capacity will be exceeded by 1987. Tyler, which can accommodate 605 kindergarten through fifth grade students, currently houses 500. If growth continues at the current rate of 10 new students a year, it could take another 10 years to reach capacity. But with half a billion dollars worth of development proposals on the drawing board for the Gainesville District, those figures may not hold, said Wildman.

Gainesville Supervisor Tony Guiffre will hold a public meeting tonight on those development proposals, which include 168 town houses as well as light industry, office space and a stone quarry.

According to School Board chairman Gerard Cleary, the land for school sites in western Prince William has not been forthcoming. School sites are usually donated to the county by developers in exchange for considerations on their projects. "Even if we had the money to build schools there, we don't have a place to put them," he said.

The School Board recently announced a $34 million building plan that includes three elementary schools and one high school. While only one of those elementary schools is slated for a site west of Interstate 66, a middle school and a high school will be needed in that area by 1990, officials say.

"We are working very closely with the county planning and development offices and they know what our needs are," Wildman said. "We want to be sure the sites will be there when we need them."

Haymarket residents and officials expressed other concerns about the accelerating growth in their town. "I support growth because I think Haymarket needs more people to care about it," said Duska Green, whose husband is planning commission vice chairman. "But our roads and parking facilities are inadequate now. If we get 170 town houses with two cars per family, that's over 300 more cars."

Some residents have expressed opposition to the proposed apartments because they could bring in low-income residents "who don't care about Haymarket," Green said.

Haymarket Mayor Gertrude Bean noted that the developments would bring county water into the town, which operates only with wells now. "The well water has lots of iron in it and that causes lots of problems."

The developer proposing the town houses is David Tinkham of Dranesville. Ivan Winston, a Roanoke developer has proposed the apartments.