Mayor Marion Barry yesterday ordered a two-month study of the impact of the controversial 6 percent gasoline tax he and the City Council imposed last month, and indicated he might recommend lowering the tax.

D.C. gasoline dealers complained bitterly after the tax was imposed on Aug. 1 that their business had declined substantially, as drivers patronized stations in suburban Maryland. The tax added about eight cents to the price of each gallon of gasoline.

Barry asked the council to impose the tax earlier this year as one of a series of measures to help alleviate the city's budget crisis. Barry said yesterday that if the study -- due to be completed by Dec. 1 -- shows that there has been a drop in District gasoline sales larger than the 16 percent expected, he would probably recommend lowering the tax.

Carolyn L. Smith, director of the city's Department of Finance and Revenue, said no specific figures are yet available for August gasoline sales. She did, however, produce figures that indicated that gasoline sales have generally declined during the year in both Maryland and Virginia suburbs as well as in the District, although the District has experienced a larger sales decline.