The D.C. City Council last night gave preliminary approval to a bill that would permit a 40 percent increase in the interest rate ceiling on personal and automobile loans.

The bill would readjust the city's usury rates for the first time since 1971 and make it profitable for Washington financial institutions to issue bank cards such as Visa and MasterCard.

The measure would increase the maximum permissible annual percentage rate lenders can charge for direct installment loans from 15 percent to 21 percent. All car loans financed by banks would be subject to increases.

The bill would raise the interest rate limits to 18 percent on all credit card purchases and advances. The current D.C. law allows a ceiling of 18 percent on the first $500 of such loans and 12 percent thereafter.

Until now, no bank in Washington has wanted to issue bank cards because the usury law made their issuance unprofitable. However, an official of the D.C. Bankers Association indicated recently that some Washington banks are prepared to begin issuing cards if the interest ceiling is raised to 18 percent across the board.

In other wide-ranging action last night, the council voted tentatively to:

Beef up and extend for three years a 1978 law designed to discourage real estate speculation by imposing a sliding-scale excise tax on the buying and selling of residential property strictly for profit.

Critics charged that the old law, enacted in 1978, has been difficult to enforce and has done little to discourage speculation, which tends to inflate housing costs and displace low-income families.

The bill approved last night would increase from 10 percent to 16 percent the maximum profit that a speculator could make on a residential tract bought and sold within a six-month period before having to pay an excise tax.

For the first time, speculators would be required to pay the excise tax before the city will record the deed transfer. Under present law, speculators have to file tax returns within 30 days after the new deed has been recorded, but there is nothing available to authorities to force compliance.

Moreover, the new law would impose a penalty of up to $100 for failure to file or for the late filing of a speculation tax return, even if no tax is due.

The bill, introduced by Council members David Clarke (D-Ward 1) and Wilhelmina Rolark (D-Ward 8), would exclude the sales of condominiums and cooperative apartments from its provisions, and would broaden and expand the category of property sellers exempt from the tax.

Repeal the city's 2-year-old, 8 percent sales tax on all candy, confectionery, soft drinks and chewing gum. Before the tax was levied, these items were subject only to a 2 percent District sales tax if they were sold from vending machines or were sold for immediate consumption by restaurants, lunch counters and carry-out shops. Otherwise, no tax was paid on those products.

Opponents of the tax contended that it was unfair to certain segments of the food industry. Moreover, aides to House Speaker Thomas P. (Tip) O'Neill (D-Mass), complained earlier this year that the tax discriminates against candy manufacturers, including some from his district.

The council also voted final authorization for the District to issue a maximum of $30 million in revenue bonds to finance construction projects for George Washington University -- the first time the city would approve such bonds for a tax-exempt institution.

Under terms of the bill, which was introduced at the request of Mayor Marion Barry, the city would market the tax-exempt bonds and then relend the proceeds to the university, which would use the funds to finance the "academic cluster" and facilities for the handicapped already under construction on the Foggy Bottom campus.

Also yesterday, City Council Chairman Arrington Dixon announced that he would not press for a full council hearing on a cable television bill he introduced Monday. He said that he has received assurances that council member Rolark will conduct hearings Nov. 10 on a similar bill that has been languishing in her committee for months.