A federal appeals court in Richmond rejected arguments by Alexandria officials yesterday and cleared the way for the start next month of a new system of ramp lights that will regulate traffic along Shirley Highway, one of Northern Virginia's most congested thoroughfares.

The City of Alexandria filed suit to stop the project, arguing that traffic from the ramps would back up on city streets and asking for an environmental study.

But the 4th U.S. Circuit Court of Appeals upheld an earlier decision by a U.S. District Court to permit the project to proceed. City officials said they did not think they will appeal further, but will review the appeals court's decision.

The exact starting date for the $20 million system, which will govern traffic on the portions of both Shirley Highway and I-66 inside the Beltway, has not yet been determined, the Virginia highway department said yesterday.

The Shirley Highway ramp lights were the only ones contested in court. Alexandria City Council member Carlyle C. Ring Jr. said yesterday, "The ramp metering system was conceived by the highway department in advance without any consultation with the City of Alexandria. The ramps are not long enough to make the project worthwhile."

Alexandria residents have argued that the ramp lights will favor commuters from outer suburbs already on the highway, cause long backups at entrances with lights and divert many cars onto their streets in rush hours.

But the court found that the highway department, which will be responsible for the operation and maintenance of the system, will be able to regulate the flow of traffic properly with the new system. The state contends that the ramp lights will speed traffic and reduce the number of accidents on Shirley Highway by reducing stop-and-go traffic situations.

The decision apparently closes a controversy that had lawyers for the two sides trading briefs almost since the ramp light system was first planned in 1976. Fairfax County had joined the original suit, but did not pursue it after the initial decision.

The idea behind ramp metering is to match demand to road capacity, and it has been implemented at several places across the country. Computers will monitor the stream of traffic through video monitors and sensors placed in the pavement and regulate its flow through the stop-and-go lights on the ramps.

"When traffic builds up to the point where we are in jeopardy of having it spill out onto the streets, we can cut the sensors off," said David Gehr, Northern Virginia district engineer for the highway department.

The Federal Highway Administration has provided 90 percent of the funds, and construction is complete.

In ruling for the state, the court said it could set aside the highway department's conclusions "only if they are 'arbitrary, capricious, and abuse of discretion, or otherwise not in accordance with law.' ".