Long-delayed plans to extend the Dulles access road from the Beltway to I-66 cleared one of the final hurdles last weekend, with federal officials predicting that construction on the four-lane extension could begin as early as September and be completed by mid-1984.

The only remaining obstacle is congressional approval of $29.8 million to complete the road.

At a public hearing sponsored last weekend by the Federal Aviation Administration, McLean homeowners living near the planned 3.7-mile extension asked for only minor design changes in the road.

Once completed, FAA officials say the extension could shave 10 to 15 minutes off trips between downtown Washington and Dulles Airport.

FAA officials said the only remaining obstacle is congressional approval of $29.8 million to complete the project. Congress already has appropriated $17 million of the $46.8 million needed for the entire project and area legislators were assured by the U.S. Department of Transportation last week that the remaining funds will not be cut from next year's budget.

"We're pretty well on the way to making Dulles a viable airport," said Rep. Frank Wolf (R-Va.), whose Northern Virginia congressional district includes the airport. "Once we make it easier to get there more people will want to use Dulles than want to use National Airport, especially during rush hours. I think we'll be able to get from downtown Washington to Dulles in half an hour."

With federal money for the Dulles highway extension almost a certainty, Saturday's hearing on the road's design was the last major step in a lengthy legal process that has delayed work on the extension for nearly 20 years.

The FAA bought the land for the Dulles access road in the early 1960s, planning to connect it with I-66 just north of Falls Church. But a long battle over construction of I-66 forced the FAA to end the access road at Rte. 123 near Tysons Corner.

When the go-ahead was given for I-66 four years ago, the FAA began reviewing its plan to link the Dulles Access Road with I-66.

Of major concern to homeowners in the area, however, was the impact the extension would have on their communities. An environmental impact statement, just completed last month, said the road would cause pollution in two adjacent watersheds and streams, destruction or disturbance of 105 acres of grassland and woods and increased noise at at nearby homes, parks and a school.

At the hearing Saturday, area residents reiterated concerns about noise from increased traffic, which federal officials estimate could reach 42,000 cars a day by the year 2000.

Frank Conlon, chief FAA engineer for metropolitan Washington airports, told the residents that grassy mounds and wooden fences will be erected along the sides of the road to reduce traffic noise. He said erosion control measures, restrictions on clearing open land and extension landscaping also will be used to minimize environmental damage.

Opposition from residents was fairly mild at the hearing because most neighbors of the project are resigned to its construction, according to Kaye Sloan Burke, president of the McLean Citizens Association. They also see it as a way to relieve traffic on existing streets, she said.

"This road will provide rapid access to Dulles Airport, a resource we are not taking advantage of," Burke said. "This will give people the incentive they need to get off our streets and get on a time-saving direct route."

Conlon said citizens have until April 27 to recommend further design changes for the road. After reviewing the public comments, the final design should be finished by late May some construction contracts should be awarded this summer, he said.

When complete, the road will be limited during peak hours in principal directions to airport traffic, four-passenger carpools, commuter buses and emergency vehicles. In nonrush hours, it will be open to all traffic except trucks.

The Dulles highway extension is vigorously supported by local government officials and business leaders who believe the road will help spur economic growth in the area.

"This extension is the key to allow Dulles Airport to approach its potential as an international airport. And Dulles Airport is the key to economic development in Fairfax and Loudoun counties," said Bill Bestimt, vice president of the Fairfax County Chamber of Commerce.

Federal authorities also are counting on the Dulles highway extension to ease traffic congestion in the Tysons area, provide a direct link between I-66 and the northern leg of the Beltway, improve access to Wolf Trap Farm Park and create a right-of-way for future extension of Metrorail on the Dulles highway median strip.