Traffic on the $56.7 million Dulles Toll Road a month after its opening is only slightly under the anticipated level of 40,000 vehicles a day, Virginia highway officials said yesterday.

Philip DuMars, the toll road manager, yesterday estimated traffic on the 13-mile, four-lane road will meet projected goals by the end of the year. Tolls have climbed from $15,289 on Oct. 2, the first full day of operation, to between $18,000 and $20,000 a day, he said.

DuMars said he is "somewhat suprised" at the volume of traffic on the highway, which extends from eastern Loudoun County to the Capital Beltway and I-66. "When I-66 opened, there was just no traffic at all for the first six weeks" as motorists switched driving habits, he said.

He said the biggest toll road problems include rush-hour traffic backups at the Centerville Road intersection, two broken toll gates at the main toll plaza and the continuing construction that is expected to keep the highway's speed limit at 45 mph for an indefinite period.

DuMars also said an estimated one-quarter to one-third of the road's Washington-bound morning commuter traffic exits at Rte. 7, ostensibly to avoid paying a 50-cent toll at the main plaza. He could not estimate how much revenue is lost.

David Hess, spokesman for Washington-Dulles International Airport, said Federal Aviation Administration police have ticketed 200 motorists in the past month for using the Dulles Access Road, which is now restricted to airport traffic.

The problem of commuter use of the access highway seems "pretty well in hand," but FAA police will continue to patrol the airport road 24 hours a day, he said.