With the Nov. 1 deadline for applying to the land-use program passed, the Loudoun County commissioner of revenues office is alerting county landowners that they can still apply through Dec. 31 for land-use status for their property. A penalty of $15 per land parcel will be charged.

The land-use assessment program, which Loudoun County established in 1973 as an incentive to preserve farms and open space, allows a landowner to have his property taxed on the agricultural value of his land, rather than the "highest and best" market value, according to William Gardner, chief appraiser for the commissioner's office. The market value would likely be the value of the land when developed with residential lots, Gardner said.

To be eligible for the land-use program, landowners must have at least five acres on which they produce goods for the market, whether livestock or crops.

About 3,000 parcels of land are annually approved for the land-use program, Gardner said. As of last week, at least 150 landowners who applied last year had yet to file their applications for 1986.

After Dec. 31, Gardner said, "there is no legal way to stay in the program . After that they would have to reapply for 1986 and they would have to pay the fair market value for 1985."