The extension of the Dulles Access Highway, up in the air for more than 15 years because of uncertainly over the completion of I-66, is now expected to be on the ground within three or four years.

The three-mile extension in McLean, to connect with I-66 from where the airport highway now ends at Rte. 123, is expected to cut travel time between downtown Washington and Dulles International Airport by at least 10 to 15 minutes and even more during rush-hour, according to estimates of the Federal Aviation Administration.

But the four-lane highway, to be built along a narrow 300-foot right-of-way that is now fields, woods and community gardens, has come as a surprise to hundreds of McLean residents.

Many residents, only learning this summer of the highway extension, bought houses along the right-of-way without knowing anything more tahn that there was "just a field" behind their houses, one resident said last week. Others knew the FAA owned the land but hoped the access road extension, contingent upon I-66, would never be built. Some said they probably won't mind the road as long as the FAA builds it as a parkway, cutting down as few trees as possible, landscaping and limiting traffic on it.

But under the FAA plans, local and limited commuter traffic will be allowed on the new extension, from the Beltway to I-66. However, only car pools and buses would be permitted to use ramps there during rush hours and trucks would be prohibited at all times - similar to restictions planned for I-66 inside the Beltway.

Local and commuter traffic could enter and exit at the Beltway and Rte. 123. In addition. Fairfax County has requested the FAA to study bus-only ramps at Magarity Road, says Conlon, ramps the county might someday wish to add to feed buses into the Metro station to be built at I-66 and the Dulles Access Road.

Exactly how the Faa will keep out commuters who don't carpool is not clear, althought it is considering everything from police officers stationed daily at ramps to computers with heat sensors that can count a car's occupants. Commuters are theoretically excluded from the present access road because ramps lead only to and from the airport. However, thousands of commuters daily foil this system by driving to the airport and making a U-turn.

Virginia currently is studying the fertility of constructing a toll road just outside the lanes of the present Dulles Access Road, but sill inside the airport right of way. It would extend from Rte. 123 to Rte. 28 near Reston.

The only remaining hurdles to construction of the access road extension are funding by Congress and completion of a required draft environmental impact statement (EIS) to determine the effects the new road will have on that section of Fairfax County.

A public hearing, part of the EIS process, is expected to be held on the highway extension within the next two months, the exact date still to be set by the FAA. But little environmental impact is forseen by FAA officials since all the land has been bought, no one will be dislocated and most homes near the road were put up by builders who knew a road probably would go there.

"I don't we'll build the road if Congress gives us the money. The kind of problems there are, are ones that can be worked out," said Frank J. Conlon, chief engineer for Dulles and National airports, the only FAA-operated airports in the country.

The $19 million needed to construct the road is expected to be included in 1980 fiscal budget requests. If it is not approved next year, the road could not be completed in time to open when I-66 opens in late 1981 to 1982.

IF the FAA is given the road money, "additional public meetings will be held, during the design stage, to give us input from people who live along it," says Conlon.

The public hearing and meetings are expected to determine what the highway will look like and the extent to which trees and existing foliage along the route are retained, whether and where soundwalls and earth berms [WORD ILLEGIBLE] built or the highway is recessed below present ground levels.

A Washington Post survey of several dozen families along the access road extension last week found about half were unaware until this summer that the highway was coming at all. Most who had heard about the road had been told when they bought their houses that it was possible but unlikely it ever would be built.

"I must say the FAA appears to want to cooperate with us on the road and so we're more than willing to cooperate with them, as long as they plan to save as many trees as possible, landscape the road and do things to cut down on the noise," Paul D'Armiento, president of the Hallcrest Heights Association, said this week.

Hallcrest Heights, a subdivision of 158 houses on a hill beside what will be the Rte. 123 exit for the new access road, has more than a dozen houses with patios within a few feet of the road's right of way.

But even closer to some, and even more upsetting, says D'Armiento, is Virginia's plan not to dead end Chain Bridge Road at the access road but "to elevate it on a four-lane bridge over the Dulles Access Road," he said.

The FAA's Conlon confirmed that Virginia has "changed its plans during the past two to three years to sever Old Chain Bridge Road because of the volume of traffic in the area." The state has noe requested the FAA to build several additional ramps at Rte. 123 and a four-lane bridge over Old Chain Bridge Road to handle increased local traffic, although it plans for the moment to keep Old Chain Bridge Road and the bridge two lanes only, Conlon said.

Many homeowners are more concerned about Virginia State Highway Department plans than they are about the FAA's new road.

"What the Virginia Highway Department is doing is a disgrace. They're cutting down almost every living thing within the right-of-way for I-66," one woman said.

"The Dulles Access Road is only one of many roads we're concerned about," added Navy Capt. Darryl DeMaris of 1706 Baldwin Dr., who lives in a subdivision where residents will be within 100 feet of the four lanes of Dulles traffic. "We're also concerned about the ramps on Magarity Road and about the Virginia Highway Department widening Great Falls Street to four-lanes," a controlversial proposal that Fairfax County officials and residents have opposed unsuccessfully for more than a year.

Another road change proposed by Virginia is relocating Idlywood Road so it runs directly into Kirby Road or closer to Kirby. Idlywood now dead ends at Great Falls Street.