TThe cost of parking on two-hour meters in central Washington will rise soon. Early in March, under current city plans, it will go from 50 to 75 cents an hour, payable only in quarters.

The proposed new rates would bring the cost of parking at two-hour meters to the same 75-cent hourly level that has been charged since 1980 at one-hour meters in the downtown and congested fringe areas.

"What we're trying to do is set a single meter rate by the hour in the downtown area," D.C. Transportation Director Thomas Downs said. "This is kind of clarifying this fact."

A total of 3,900 two-hour meters will be affected, in an area extending from 17th Street SE, near the RFK Stadium-Armory complex, westward to 37th Street NW in Georgetown, and from the Potomac River north to Massachusetts Avenue, plus the area from Dupont Circle to Rock Creek Park.

Downs said the higher rates are expected to yield an additional $1.1 million for each full fiscal year. The city's total of 11,500 meters now bring in $7.1 million annually. Many outside the central area cost 50 cents an hour.

Officially, the price increase announcement is a notice by Downs that he intends to adopt the higher rates sometime after March 5. Those who want to comment or protest may write him at Room 508, 415 12th St. NW.