Thousands of District of Columbia homeowners are paying more taxes than necessary because their homesites are composed of two separate lots, chief D.C. assessor Donald R. Beach said yesterday.

These homeowners are penalized two ways, he said. They can claim the $9,000 homeowner's exemption to reduce the assessment only on one of the lots, which is being taxed this year at the rate of $1.54 for each $100 of valuation. The second lot, classified as "vacant," is taxed by law at the commercial rate of $1.83 per $100.

In Hillcrest, a far Southeast Washington neighborhood, the owner of a home located on two lots, with a total assessed valuation of $63,315, would pay $889 at the current tax rates. If the two lots were combined into one, the tax would drop by $53, to $836.

Beach said his office in the D.C. Department of Finance and Revenue can combine the lots at a taxpayer's request, but probably not in time for next fall's tax bills. A speedier way would be for the City Council to amend the law to apply the homeowner's exemption and the residential tax rate to such properties, Beach said.