More than 26,000 District of Columbia taxpayers have been notified that they must pay $5 million in personal property tax installments this month, a month earlier than they have done in past years.

Carolyn L. Smith, director of the D.C. Department of Finance and Revenue, said the installments previously due Oct. 15 are now due on Sept. 15, with each individual payment averaging $192.

That means the affected District taxpayers face a double tax bite on the new date, since the first installment on the 1980-81 real estate taxes -- totaling about $225 million -- also are due at the same time.

Ater notices of the new date were mailed to the taxpayers this month, Smith said her office received about 125 complaints, mostly by telephone.

The quarterly income tax payments must be made by persons who in general earn more than $1,000 a year that is not subject to withholding from paychecks. e

Smith said the new dates for quarterly installments were required by the D.C. tax law passed by the City Council in July. It took effect Aug. 1. dIt is a little-noticed provision of th same law that imposed a gasoline sales tax and raised the level of a number of existing city taxes.

The income tax payments made this month will produce a windfall of $5 million to the city Treasury near the end of the fisca year, which ends Sept. 30, helping ease the city's projected $125 million deficit.

Even without the windfall, Smith said she would have proposed the changed dates, since they will now match the payment timetable required for many of the same taxpayers under the federal income tax law.

Previously, installments were due on the 15th of July, October and January with the annual tax return and final payment due April 15. The new schedule is June, September and December, with the final return still due April 15.