The long-planned widening of Rte. 1 through Crystal City in Arlington moved closer to construction yesterday with the County Board's unanimous, but heavily conditional, approval of design features for the severely congested road.

After four hours of debate and residents' comments, the board adopted a detailed design package that covers issues ranging from landscaping, pedestrian walkways and the speed limit on the South Arlington thoroughfare to sign sizes and curb gradings.

Residents pointed out that those details are at the root of their concerns about safety, air and noise pollution, and traffic congestion on neighboring streets.

Board members linked state implementation of the approved design details to county cooperation with a future state highway department effort to lift a 1976 federal court injunction barring work on Rte. 1.

Civic groups and two hotels successfully sued in the past to block construction of the proposed Interstate 595 spur, from Shirley Highway to the National Airport viaduct, which would have replaced Rte. 1 with an elevated highway.

The court ruled that the state failed to conduct proper hearings on the proposed road and ordered the state highway department to begin the hearing process again. Since then, the state has modified its plans. A highway official said last month that he doubted the court would lift its injunction if the County Board rejected the revised plans.

The new plan calls for a $37 million, 1.8-mile project in which Rte. 1 would be widened from four to six lanes, plus turning lanes, from South 12th Street in Arlington's Crystal City to just north of Reed Avenue in Alexandria.

The state also must win the approval of the Alexandria City Council, which is scheduled to vote on the city's portion of the road this week amid growing opposition from residents. In addition, the plan needs the endorsement of the Virginia Highway and Transportation Commission on Dec. 20, before the highway department seeks to get the injunction lifted in January. If the court lifts the injunction, work on the first phase could begin next summer.

"We're not asking the state to consider things. We're asking the state to do things," said Arlington County Board member Albert C. Eisenberg.

Board Vice Chairman John G. Milliken, noting that the injunction might not be lifted without the board's agreement and that the state already has agreed to many details, added, "The leverage is there if the state goes back on its word."

Although the road's widening to six lanes was decided almost three years ago, several residents lobbied again yesterday in favor of a four-lane project.

"This highway could be beautiful just the way it is. The six-lane version is devoted to solving a private developer's problems from his massive development," said Dick Herbst, a nearby resident, referring to the Charles E. Smith Co.'s Crystal City high-rise empire.