Just about the only issues left in the 21-year-old citizens' battle to prevent construction of I-66 through Arlington are these: How many trees will be spared by bulldozers now clearing the 300-foot to 2,000-foot-wide right of way and how many new trees will Virginia plant to make I-66 the scenic parkway promised by state and federal officials?

A recent tour of the route found many residents unhappy with the dust and noise of construction but pleased that sound barriers will be built, similar to those now going up along the Beltway, and that the road will be depressed rather than elevated through most neighborhoods.

But they also complained that the Virginia Highway Department is marching through Arlington the way Sherman marched through Georgia, leaving few trees for the parkway. Their protests grew so great last spring and summer that U.S. Rep. Joseph L. Fisher (D-Va.) met with President Carter to discuss I-66, and Federal Highway Administration (FHA) officials were called before a congressional committee. Carter suggested that the FHA, which is paying 90 percent of the construction costs, consult Eugene Odom, a nationally known ecologist from Georgia.

As recommended by Odom, Virginia highway officials have since hired an environmentalist Keith Argow of Trout Unlimited, to monitor I-66 construction. Argow is the first environmentalist hired to review a state highway project.

State officials now are proclaiming that I-66, at least inside the Beltway, will be the most heavily landscaped and aesthetically designed highway ever built in Virginia.

But Argow has little vegetation left to protect, says Marianne Karyades of Contact, the chief environmentalist group opposing I-66 work. The state effort is "too little, too late," she says.

More than 75 percent of the clearing for the highway already is done. Eight of the nine construction projects are under way and most are to be completed next year. Only one section - in Rosslyn - has yet to have a contract awarded. That section is expected to be finished, and the entire road opened, in 1982.

A special citizen information trailer, under Argow's direction, will be opened in about two weeks, say highway officials, at the intersection of Fairfax Drive, Glebe Road and N. Vermont Street. Maps and detailed information on all nine construction projects will be available.

If there has been little success so far in preserving trees along the I-66 right-of-way, there was a small citizen triumph recently when state highway officials were persuaded they need not wait one, two or three years before landscaping the huge dirt embankments being pushed around in constructing the four-lane road.

With a little help from the House Public Works Committee and federal highway administrators, residents of Circle Terrace condominiums along Spout Run convinced Virginia higway officials that it is possible to landscape a highway as soon as it is built.

"We feel it's an outmoded concept to leave land unlandscaped for three years while it settles . . . as Virginia did along Shirley Highway," said Lincoln McCurdy, a trade specialist for the Department of Commerce and a member of the Circle Terrace I-66 committee.

The early landscaping idea had been expanded beyond the Spout Run area to include all nine construction projects.

Not only will McCurdy and his fellow residents see new trees and shrubs this fall along their section of I-66, but they convinced highway officials to save 10 large trees - by taking the officials on a walking tour of the site just before tree cutting began.

To make I-66 into a scenic "parkway" will require extensive landscaping, especially since so few trees have been left in the right of way.

When William Coleman, former U.S. Transportation secretary, approved a truckless, four-lane I-66 last year (instead of the six- to eight-lane "super highway" long proposed by Virginia), his decision provided that the "construction of the I-66 right-of-way, insofar as possible, be similar to that of the George Washington Memorial Parkway."

But ecologist Odom expressed "great skepticism" that construction companies would save many existing trees and criticized the proposed government landscaping plans for I-66 as "amateurish . . . and token."

Odom recommended hiring "a really first-class landscape design firm to do the job" and added: "After all, some of the money saved by not building the extra four lanes . . . should be put into making the corridor a really attractive example of what can be done to create an urban parkway rather than the usual commercial interstate." Construction of the 10-mile section of I-66, excluding landscaping, is expected to cost $150-$200 million.

Under the Coleman decision, trucks will be permanently prohibited from I-66, and buses and car pools will be the only vehicles allowed during rush hours. Traffic will be controlled to limit congestion on I-66 and the Roosevelt Bridge, which will connect the highway with Washington.

Virtually all the 10-mile section I-66 will be monitored by closed-circuit television, and sensors will be built into the highway to tell computers how heavy traffic is and when and where there is a vehicle breakdown, according to David Gehr, regional transportation engineer for Virginia. During rush hour, state police will arrest drivers of cars with fewer than four occupants, as is done now in the car-pool and bus lanes on Shirley Highway. Geher said no other highway in America will be as closely watched and monitored as I-66 inside the Beltway.

Among those watching will be the thousands of Arlington residents living within sight and sound of the new road. Most moved into their homes knowing I-66 might be built and hoping it wouldn't. "But we didn't perceive it would be as bad as it is," said Vickie Cavazos, who lives very near the future Beltway exit onto I-66.

The exit ramp is on a hill of dirt higher than the Cavazos' house and will be topped with a 10-foot-high wooden noise barrier. Last summer, said Cavazos, there was only a stream and quiet woods filled with birds. "And now we're stuck here. No one would buy our house. The house next door has been for sale now for a year and a half. However, the county did lower our tax assessment."

About 500 families have been relocated since Virginia decided to build I-66 in the 1950s, some as recently as this year. Among those relocated this year was the Brodie family, whose red brick house at the end of Arlington's Nicholas Street is about to be engulfed by a 40-foot-high embankment.

"The people I feel sorry for are our neighbors who have to live with I-66," says Bea Brodie, who now lives in Herndon. "But for the people in Fairfax County, like us now, I-66 is going to be great."

Virginia highway officials predict that I-66 will cut communting time in half, at least for those in buses and car pools.