After 20 years of bitter court fights, the Virginia highway department yesterday began cutting down trees to build Interstate Rte, 66 from the Capital Beltway to the Potomac River.

Moments after U.S. District Court Judge Oren R. Lewis in Alexandria denied an injunction sought by highway opponents to block construction of the four-lane, 9.7-mile road, a four-man crew started chain saws and toppled trees just outside the Beltway where the superhighway now abruptly ends.

The crew had been waiting at the construction site since 8 a.m. for Lewis' decision and killed the time by surveying the area and "illegible." According to the crew superintendent, Ronald McGurk, of James Julian, Inc., in Wilmington, Del. The firm has the contract to build the first 117 miles of the 1.66 extension, from the Beltway Rte, 7 (Leesburg Pike).

McGurk said he and his crew would spend most of this week clearing trees and moving dirt.

McGurk said he and his crew would spend most of this week clearing trees and moving dirt.

In Richmond, officials of the Virginia Department of Highways and Transportation, reacted to Lewis' decision with a mixture of relief and determination.

"I don't intend to stop unless ordered to by the courts," said a triumphant John E. Harwood, the state highway commissioner. "This is the farthest we have ever got."

But he cautioned that "I still see some roadblocks ahead" and that he, for one, viewed an appeal by highway opponents to the U.S. 4th Circuit Court of Appeals in Richmond as a certainty.

In court, Lewis said he would grant the injunction filed by a coalition of civic association on one condition, if it posted a $500,000 bond.

Lawrence latto, attorney for the chief nati-66 group, the Arlington Coalition of Transportation, which relies on voluntary contributions, said, "I think Lewis recognized we were incapable of raising the

Latto said the coalition, which opposes the 1.66 construction on environment grounds, would file an immediate appeal of Lewis' ruling with the 4th Circuit Court. Last Friday Lewis affirmed the decisions of two U.S. secretaries of transportation that the $170-million highway should be built.

John Beall, the assistant attorney general who acted as lawyer for the highway department, said he expected the appeals court would hear the civic associations' request for an injunction blocking construction pending an appeal within the next two weeks.

In his ruling yesterday Lewis said that the civic associations had not shown that construction of the roadway would cause them irreparable injury.

Lewis once before approved construction of the highway, but the Fourth Circuit ruled that the state highway department had to hold extensive public hearings on the road's environmental impact on people who would live along its route in Fairfax and Arlington counties.

The highway department subsequently narrowed its proposed highway from as many as eight lanes it. Some spots to four, and banned trucks altogether.

This time the highway department quietly laid plans to begin construction of the road immediately after Lewis' decision. Actually, crews could have begun work on the road late Friday afternoon after Lewis' Friday decision, but Harwood decided to have the crews wait until yesterday, a lawyer for the state said.

State officials have made no secret of their impatience over delays in building the road and there was some suggestion that work begin on Saturday. Harwood ruled that out on Friday "because it's hard to start anything on Saturday.

Instead, he asked Donald Keith, the department's resident engineer in Fairfax, to tell the Julian company to have its crew on the site yesterday morning. "We've had our contractor on a string for a long time now, "Harwood said.

But, warned that another hearing before Lewis was likely yesterday morning, Harwood directed the crews wait at the site until they heard from the state's lawyers.

There was no celebrating yesterday at either the office of Gov. Mills E. Godwin, a long-time highway supporter, or at the highway department. "Of course, we're very happy and we to all concerned," Harwood said.

Knowing the possibilty of losing the case in the appeals court, Harwood said any celebration would be premature."My celebration was a sigh," said state Assistant Attorney General Valentine W. Southall.

One reason the state decided to begin construction immediately was its belief that any further delay would only bosst the highway's costs still higher Southall said. Furthermore, officials noted that there was a one-week delayed between the time the road's opponents announced they were appealing a previous Lewis order and the arrival of their appeals petition at the Fourth Circuit.

The highway is designed so that its median strip can accommodate an extentsion of the Metro subway, and some $30 million in construction money is dedicated to subway preparation. However, there is some question as to whether that rail line will ever be built.

At the moment, a Metro tunnel is under construction through Arlington from the now-operating Rosslyn station. The tunnel generally follows the route of Wilson Boulevard and Fairfax Drive to Glebe Road. Just west of Glebe Road the line is scheduled to come out of the tunnel and run down the 1.66 median to Nutley Road in Vienna.

However, money to build the project is assured only as far as Glebe Road, close to the so-called Ballston station. Subway operations from Ballston to Rosslyn are scheduled to begin in June, 1979.