The D.C. City Council's Finance and Revenue Committee voted 4 to 1 Tuesday to extend a 1978 anti-real estate speculation law for another three years and to add provisions to make it easier to enforce.

The law imposes a sliding scale excise tax on speculators who buy and sell residential property for profit. Critics say the law has been difficult to enforce and has done little to discourage speculation, which tends to inflate housing costs, disrupt neighborhoods and displace low-income families.

The bill approved by the committee yesterday would increase from 10 percent to 16 percent the maximum profit that a speculator could make on a residential property, that he bought and sold within a six-month period, before he had to pay an excise tax.

Also, for the first time, speculators would be required to pay the excise tax before the city will record the deed transfer. Until how, speculators had to file tax returns within 30 days after the new deed had been recorded, but there was nothing that forced them to comply.

The bill also broadened and expanded the category of property sellers who are exempt from paying the tax.

Council member Betty Ann Kane (D-At Large) opposed the overall measure, which was supported by David Clarke (D-Ward 1), the bill's author, Polly Shackleton (D-Ward 3), chairman John A. Wilson (D-Ward 2), and H, R. Crawford (D-Ward 7).