Mayor Marion Barry has proposed raising the annual license tag fees for most vehicles in the District from $35 to $48, an increase that would fall primarily on owners of small vehicles while some who drive older, larger vehicles would pay less.

Barry also wants to scrap the city's system of charging a graduated excise tax of 4 to 7 percent on first-time auto registrations in the city in favor of a straight 6 percent tax -- a move that also would affect owners of small cars more than others.

In a letter to the City Council asking for authority to impose the new fee and tax system in time for next year's tag renewals, Barry said the increases -- which would raise about $3 million more per year -- were necessary to help offset a severe shortfall in revenue that the city expects because of the nation's flagging economy.

The new fee structure would eliminate the system of preferential treatment the city established in 1977 to encourage the use of smaller, more fuel-efficient cars instead of older, gas-guzzling vehicles that also spewed more pollution into the air.

"I believe that the District no longer needs to encourage the buying of small cars . . . ," Barry's letter stated. "The price of fuel today and the always rising cost of living has provided all the incentive for small cars that is really necessary."

The owner of a small subcompact car, such as a Chevrolet Chevette or a Ford Escort, now pays $35 in annual license tag fees but would pay $48 under the mayor's proposal.

The owner of a car weighing 3,500 pounds or more, such as a Cadillac Eldorado or a Lincoln Continental, now pays $68 a year but would pay only $60 under Barry's plan.

Owners of some older cars that weigh more than 4,000 pounds now pay $76 a year for their license tags, but would pay only the $60 under the proposed plan.

The initial excise tax for most large cars would be unchanged. But the tax on registering a small car would increase sharply from 4 percent of the car's fair market value to 6 percent -- an increase in some cases of $100 or more.

Barry asked the council to approve the changes -- which would affect about 210,000 of the approximately 300,000 registered vehicles in the city, with trucks, motorcycles and antique cars not affected -- by passing emergency legislation to impose the new costs starting in February.

March 31 is the date by which all cars registered in the District must have new license tags, and about 75 percent of the city's motorists re-register their cars each year between Feb. 1 and the deadline, city transportation officials said.

If the measure were handled routinely by the council, the new fees could not go into effect until after March because of a 30-day mandatory congressional review period for all city legislation except measures passed under its emergency authority.

Annette Samuels, Barry's press spokeswoman, said the mayor could not put a dollar amount on the "severe" revenue drop. "We are looking at revenues for 1983. We do not have figures at this time," Samuels said. "We are living in a recessionary time and one can expect revenues to drop sharply."

The prospects for Barry's proposal in the City Council were unclear yesterday. John A. Wilson (D-Ward 2), chairman of the council's finance and revenue committee, said he believed it was the first of several changes Barry would have to make in this year's budget because of overly optimistic revenue forecasts during the past election year.

Wilson, a frequent critic of the mayor's handling of tax issues, said he wants to hold a public hearing on the increases before the council acts. He said the emergency legislation was not assigned to his committee. "I assume that was being done" in a deliberate attempt to avoid his committee, Wilson said.

Thomas Downs, director of the D.C. Department of Transportation, said the proposed changes are part of a long-range plan to adjust the city's fees for inflation and to streamline the vehicle registration process.

The city now takes in about $14 million a year in passenger vehicle registration fees and would collect about $17 million under Barry's proposal.