Q) I have just received a notice of assessment for my property in the District of Columbia. The District has determined that my property has increased significantly in value, and I believe that this assessment is much higher than the real worth of my property. What can I do?

A)The D.C. Department of Finance and Revenue has again mailed out notices of proposed real property assessments for fiscal 1989 to all property owners in the city. The assessment is used as the basis for determining the annual real estate tax bill.

Real estate taxes in the District are paid twice a year. The District's fiscal year begins on July 1 and ends on June 30. The first half's taxes are due on Sept. 15 of each year and the second half taxes are due by March 31.

The notice of proposed real property assessment that you received will be the basis for your real estate taxes next year. Do not forget that the second-half taxes for fiscal 1988 are due by the end of this month.

Although the real property tax rate for fiscal 1989 has not been set yet, it is helpful to know what the tax rate was for this year. It may well be that the City Council will use the same rate next year.

The tax rate for fiscal 1988 was $1.22 per $100 of assessed value for Class 1 properties; $1.54 for Class 2 properties; $1.82 for Class 3, and $2.03 for Class 4.

Generally speaking, Class 1 properties include improved residential property that has no more than five dwelling units and is occupied by the owner. The clas also includes owner-occupied condominiums and cooperative apartments in which 50 percent of the dwelling units are occupied by the shareholders.

Class 2 is improved real property used solely for nontransient dwelling purposes, and includes cooperative apartments in which fewer than 50 percent of the dwelling units are occupied by shareholders.

Class 3 contains commercial property that houses transients. Included in this class are hotels, motels and inns.

Class 4 includes any improved property that does not fall into the previous classes.

Keep in mind that D.C. real property assessors based your proposed assessment on what they estimated your property's worth to be on Jan. 1.

"In making this estimate, the assessors took into account information such as recent sales of similar properties, current building cost and any income that is produced, or might be produced, from real property," the District says.If you do not believe that the assessment accurately reflects the value of your property, you may file an appeal with the Board of Equalization and Review. Appeals must be postmarked or delivered by April 15.

Before you decide to appeal, however, do a little homework. Examine the assessments of comparable properties. The assessment rules can be reviewed in the lobby at the District Building, at 1350 Pennsylvania Ave. NW; at the Municipal Center at 300 Indiana Ave. NW, outside room 2152, and at some libraries.

Next, contact the Valuation and Assessment office (727-6460) and talk with the assessor who actually reviewed your property.

The assessor has the authority to adjust your assessment administratively if there is an obvious mathematical or data processing error, if there has been recent damage to your property or if the property record kept in the assessor's office is incorrect.

If the assessor does not adjust your assessment, or if you remain unconvinced of the accuracy of the results, you may file an appeal. You may obtain an appeal form from any D.C. public library, or by calling 727-6860.

My advice to anyone contemplating an appeal: Ask yourself if you are willing to sell your property for the amount assessed by the D.C. government. All too often, although the assessment may appear high, in reality it is much lower than you know the property is worth. Benny L. Kass is a Washington attorney. For a free copy of the booklet "A Guide to Settlement on Your New Home," send a self-addressed stamped envelope to Benny L. Kass, Suite 1100, 1050 17th St. NW, Washington, D.C. 20036. Readers may also send questions to him at that address.