Officials at Washington Dulles International Airport said they plan within the next two months to provide 300 additional parking spaces opposite the main terminal to ease parking problems for commuters and weekend travelers.

Airport officials also plan to operate a valet service for passengers who will not have time to leave their car in one of three long-term, satellite parking lots and take a 4-minute shuttle bus ride to the main terminal.

Thomas Morr, president of the Washington Dulles Task Force, a group helping to plan the airport's growth, said the valet service is designed for travelers in a hurry or those who will not mind paying a few extra dollars for parking. Officials have not yet determined the cost of the valet parking.

"Someone can pull up to the main terminal, check in with their baggage and airline ticket and give their keys to someone else to park the car," Morr said.

When these passengers return to Dulles, they will take a short shuttle bus ride to the special valet parking area, located adjacent to the main terminal, and avoid the main lot's often lengthy exit lines.

The airport will gain the 300 additional parking spots by using space now reserved for rental cars in the $6-per-day parking lot. Rental cars will be moved to a site near the satellite parking facilities, one-half mile from the main terminal.

In an effort to relieve backups of traffic exiting Dulles, officials are advising passengers to use one of the airport's four satellite parking lots. Dexter Davis, airport manager, said there is "a problem with cars queuing up at the exit from the main parking lot" during its busiest hours, which are from 3 p.m. to about 7:30 p.m., particularly on Fridays and Sundays.

Passengers driving out of the lots closest to the terminal -- the hourly parking lot, which has 350 spaces, and the daily parking lot, which has 3,370 spaces -- all have to go through one exit, creating a bottleneck. The satellite lots, however, have a separate exit and less traffic.

Davis said that most travelers are not aware of the airport's satellite parking lots, which are serviced by shuttle buses that run every 10 to 15 minutes to the main terminal. He said drivers sometimes have to wait as much as 30 minutes at the exit booths to the parking lots near the main terminal.

Morr said the hourly parking lot, which is directly opposite the main terminal, is intended for persons traveling for brief periods. The rate there is $1.50 per hour or $18 per day.

The daily parking lot, just beyond the hourly lot, is designed for commuters or weekend travelers -- "the people who expect to come back in a day or two," said Morr. The daily area rate is $6 per day or $1.50 per hour.

The charge in the satellite parking areas, which are mainly for travelers who expect to be away for more than one week, is $3 per day. Officials said the areas' exit booths always have rapid turnover.

Dulles officials expect to handle more than 4 million passengers this year, more than 30 percent over 1984 figures. The airport's six parking areas have a total of close to 10,000 parking spaces, 49 of which are restricted to members of Congress and diplomats.

Davis said the Federal Aviation Administration, which runs the airport, will do "whatever it takes" to allow passengers quick and easy entry and exit.

In addition to enlarging its parking facilities to handle the increased traffic, Davis said, the airport has plans to expand the current fleet of seven 19-passenger shuttle buses.

A radio advisory system is planned for early 1986 to give drivers up-to-date parking and traffic information by the time they reach Reston.