When harried commuters drive Shirley Highway late next year, Big Brother will be watching.

Nearly every inch of the 9.6-mile roadway from the Capital Beltway to the District will be monitored by closed-circuit television cameras and wire pavement sensors.

Computers will work behind the scenes to flash messages on signs to motorists, reverse the direction of some lanes and prevent too many cars from getting on the road at once.

This futuristic, $20 million system, which also includes similar controls for I-66, will make Shirley Highway (I-395), Washington's busiest commuter artery, one of the most sophisticated in the nation.

Rush-hour testing of the operation is set to begin in December before the system's scheduled May 1983 completion date.

Virginia highway officials hope the I-395 rush-hour commuting time from the beltway to the District will be slashed 25 percent and accidents "significantly" reduced, said Thomas Farley, the Virginia highway engineer who will operate the system. "We'll be able to smooth it out somewhat so that the peak-hour traffic jams are less than what we're experiencing today."

But automation is also expected to bring cries of dismay from impatient commuters waiting behind traffic signals installed on many of the highways' on-ramps, not to mention start-up problems Virginia engineers predict will cause "minor inconveniences" during the 6:30 a.m. to 9 a.m. rush period and the 3:30 p.m. to 7 p.m. crunch.

The Virginia system, financed by 90 percent federal and 10 percent state funds, is similar to a system that regulates some Southern California highways and has been credited with reducing traffic delays, pollution, gasoline consumption and accidents.

"It is not a panacea," said California traffic engineer Charles Sweet, "but it should even out the demand" by making motorists wait behind signals on entrances at moments when the roadway is especially crowded. "Any time you smooth out the flow of traffic, even though you increase the volume, you reduce the number of accidents."

For Virginia, the result could be vintage science fiction -- or an expensive scheme costing a projected $1 million a year in state highway department funds to operate but falling short of its Utopian promise.

"I think it's absolutely bizarre," said WMAL traffic reporter "Capt. Dan" Rosenson of the system. "I doubt that it will help anywhere near to the amount of dollars that are being put on it."

The system could be overwhelmed with too much traffic -- or engineers could choose to allow cars to pile up behind on-ramp signals and spill onto nearby local streets, clogging traffic there. "Certainly, there is some concern about that," Farley said.

"The ramp metering is not trying to do away with the congestion on Shirley Highway," warned David R. Gehr, a division administrator in the Virginia Highway Department.

On an average workday, 101,000 vehicles use Shirley Highway from the 14th Street bridges through Springfield, with the flow at the bridges reaching 172,000 vehicles, local officials said.

During the peak of rush hour the new ramp signal lights will almost always be green because traffic is moving so slowly, Farley said. But during just-off peak times, he said, ramp signals will play a vital role by only allowing cars on the roads when the computer predicts there will be the most room for them.

Besides reducing unnecessary slowdowns and knots of heavy traffic when overall traffic is light, signals are supposed to cut down on rear-end collisions at on-ramps, Farley said.

Engineers plan to run the system 16 hours every day, using an array of sophisticated equipment that includes:

* On-ramp controls -- Traffic signals will vary between red and green according to traffic conditions monitored by counters buried in the highway pavement. Each ramp will get an equal amount of red light time during peak periods, Farley said. Engineers will be warned when waiting cars pile up near the end of a ramp. Some entrances are being widened to two lanes to accommodate more cars.

* Special lanes -- Two lanes on Shirley Highway reserved for cars and buses with four or more passengers will continue to reverse direction each day to match the the flow of rush-hour traffic. But automation will cut the time to switch lane direction from several hours to about 30 minutes and will allow engineers to vary the exact time lane direction is changed, Farley said. Special lanes will switch direction at the same time each day when the system begins operation.

Lanes moving toward Washington on I-66 inside the Capital Beltway in the morning and away from the city in the afternoon also will be limited to cars and buses with four or more passengers.

* Variable-message signs -- To warn commuters of lane closings and traffic tie-ups, road signs will flash messages automatically determined by a central computer in an office near the Pentagon. Other signs near on-ramps will say which way special lanes are headed. Engineers can override the computer and post a message themselves.

* Closed circuit television -- Cameras will allow engineers to check up on computer decisions and enable workers warned by the computer of an accident to describe the situation to police.

For example, engineers will be warned when computers detect a sudden traffic stoppage in a lane and told which TV camera to use to see the situation close-up. Only key parts of I-66 will be covered by camera.