Prince William County will get more than a million dollars next year because the Virginia General Assembly closed a loophole in a program designed to help farmers keep their land.

Farmland, forests and certain types of open space, including golf courses and parks, are eligible for a "use value taxation" program, in which tax assessments are based on the land's use rather than its market value. For prime development land, the use value can be as little as one-fiftieth of the market value.

Most states use such tax breaks to encourage preservation of farms and forests, but when developers purchase large tracts, they sometimes use the program to minimize tax payments on land they are not ready to develop.

Developers must pay back five years of their tax savings if they get the land rezoned for development, but until this year, some land zoned for commercial and residential use before 1980 was included in the program.

The General Assembly voted in the spring to remove that property from the use value program.

As a result, the owners of 32 Prince William parcels, assessed for a total of $90.5 million, will pay $1.2 million more in taxes next year, said Lurty Houff, real estate assessment manager.

Loudoun County, where roughly two-thirds of all land is in the use value program, excluded land zoned for development from its program in 1987, so it was not affected by the legislation.

Fairfax has a somewhat different program that was not affected by the change; Arlington and Alexandria do not have land use programs.