Officials of 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 four-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. "It will be much easier to catch a plane if you're late."

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 often lengthy exit lines at the main lot.

The airport will gain the 300 additional parking spots in front of the main terminal 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, a half-mile from the main terminal.

In an effort to relieve traffic backups getting out of 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 located closest to the terminal -- the hourly parking lot, which has 297 public spaces, and the daily parking lot, which has 3,370 spaces -- all have to go through one exit, which creates a bottleneck. The satellite lots, however, have separate exits and less traffic.

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

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

The daily parking lot, located 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. Airport officials said there is always a rapid turnover at those exit booths.

"The rates of the parking lots are set to discourage those from misusing the hourly parking lot," said Morr.

Dulles officials expect to handle more than 4 million passengers this year, more than 30 percent over 1984 figures. There are nearly 10,000 parking spaces in the airport's six parking areas, 53 of which are reserved for members of Congress and diplomats.

Davis said the Federal Aviation Administration, which runs the airport, will do "whatever it takes" to provide passengers with quick and easy passage into and out of the facility.

In addition to enlarging its parking facilities to meet the surge in airport traffic, Davis said, there are plans to expand the current fleet of seven 19-passenger shuttle buses.

"We will have three new 27-passenger shuttle buses soon to service the satellite parking lots and if that's not enough, we'll buy more," he said. Additional baggage claim belts are now being built in the airport's lower level to handle the heavier passenger load. A radio advisory system is planned for early 1986. Drivers who tune in will get up-to-date parking and traffic information by the time they reach Reston, about five miles to the east.

Dulles officials plan to build at least two more runways to accommodate an estimated 40 million passengers a year. "We're at only 10 percent of our ultimate development right now," Davis said.