The $20-million computerized, televised traffic control system now being installed on I-66 and I-395 is being accused of favoritism even before it is turned on, because it will restrict access by motorists inside the Beltway.

When traffic is heavy on the two interstate roads, new stop lights at all access ramps inside the Beltway will limit the number of entering cars, thus preventing solid lines of merging ramp traffic from interrupting the main flow of traffic on the highway.

Ramp metering has increased rush-hour traffic speeds by 25 percent and reduced traffic accidents by 3C percent in cities where it is now in use, according to Virginia highway officials. They believe it could do the same on I-395, which now has three-hour-long morning traffic jams starting at 6:30 a.m.

When I-66 opens three weeks from today it will be restricted to car pools and buses during rush hour and it is expected there will be no traffic jams, at least until the select group of HOVs (high occupancy vehicles) is forced to merge with hoi polloi of ordinary auto commuters at Roosevelt Bridge.

While ramp meters, television surveillance, variable message signs and electronic road sensors are being installed on both I-66 and I-395 inside the Beltway, their major impact will be on I-395, since it has heavy traffic.

In Alexandria, with four I-395 intersections, the City Council last week was on the verge of trying to block operation of the metered ramps, but then postponed action until city transportation officials report back on the issue at next week's meeting. Council members were concerned about charges that the system is balanced against city residents.

State Del. Bernard S. Cohen (D-Alex.) told the council the system has worked well in other cities, but State Sen. Wiley Mitchell (R-Alex.) urged the council to fight it because he said "there is nothing" in it to benefit Alexandria.

Virginia highway engineer Thomas Farley, who will oversee the operation of a computer and 15 people needed to operate the system 16 hours a day on both highways, said local officials are unnecessarily worrying themselves about the access question.

"The whole point of this is to make traffic run more smoothly and safely, which will benefit all motorists, urban and suburban... and if there are backups at the entrance ramps, which are being widened in many places to two lanes, then we can always allow more cars in, or even stop metering completely and go back to" the current situation.

In fact, when traffic on I-395 is at its worst, bumper-to-bumper and crawling along, there is little that ramp meters can do to improve things, Farley admits. "The main benefit will be in the shoulder periods, possibly allowing us to postpone the start of the morning logjams from 6:30 to 7 a.m."

The ramp lights will be controlled by computer to allow between five and 15 cars to enter the highway each minute.

But the ramp lights can be overridden manually, Farley said. Pavement sensors, installed all along I-66 as well as on I-66 and I-395 ramps, count traffic and tell the computer when a ramp has filled up and might cause a traffic backup on nearby streets. Operators also will be able to view the traffic situation at the ramps by closed-circuit television.

Since most of the high-tech electronic system will not be operative on I-66 when it opens Dec. 22, Virginia State Police will be stationed at the three inbound entrance ramps inside the Beltway in the morning rush hour and at the four exit ramps in the evening. Their primary purpose will be to stop any trucks with six or more wheels and all vehicles with fewer than four occupants.

But for the moment, said Farley, the police also will act as the ramp meters.