Precisely at 7:30 each morning, warning lights flick on across signs above the 22 roads leading into the central business district of this fabled world trading city. They read: "Restricted Zone - in Operation."

From that moment until 10:15 a.m., any automobile entering downtown Singapore must have a pre-purchased $1.60-a-day sticker on its windshield. Corporate cars have to pay twice as much. Not even diplomats or high government officials escatpe the net. The only exempted vehicles are buses, some delivery trucks and car-pooling vehicles with four or more persons inside.

Singapore's so-called "area licensing system" - ALS - is the first major experiment by any city to control the torrents of traffic that clog streets, pollute the air and cause immense waste of fuels in the central business areas of developed and underdeveloped countries alike.

The Singapore results: The number of cars entering the downtown district during the morning rush hour has dropped by an astonishing 73 per cent. Car-pooling has increased by 80 per cent. Buses run more frequently and on time through the unclogged streets, cutting commuters' delay and frustration. There's been a sharp drop in carbon monoxide air pollution, a welcome relief in a hot, hazy city only 86 miles from the equator. People who walk to work enjoy cleaner air and are less exposed to hazards of heavy traffic.

The Singapore system has been in effect about two years. World Bank economists who've been monitoring it carefully declare it a "clear success" that "might be a way to break the spiral of increasing congestion and decreasing public transportation service" in cities around the world.

The U.S. Transportation Department believes the plan is promising enough to warrant experimentation in American cities - and actually has some demonstration money on hand to aid any willing to give the system a try.

The stores and shops of downtown Singapore haven't suffered because most don't open until 10 a.m. - just before ALS is lifted each day. Shoppers aren't affected expect fo rthe higher parking fees that have been imposed. The only major disappointments have been the failure of fringe parking lots, served by shuttle buses, to attract many users, and less than a full "mirror effect" in reduced evening rush-hour traffic. (Cross-city commuters don't bother to use a circumferential road, as they do in the morning to avoid the ALS fee, and some commuters have their families drive into town to pick them up.)

A public-opinion poll, sponsored by the World Bank, showed a great majority of Singapore residents approved of the ALS plan. They cited improvements in travel time and shopping conditions and a reduction in noise levels.

One attractive feature of the Singapore plan, recommending it ot other cities, is its flexibility. The hours of travel restriction and the boundaries of the restricted area can be changed with ease. Another advantage is cost: The capital cost is minimal, and in Singapore the monthly fees from drivers willing to buy the ALS stickers have been 10 times the cost of enforcement.

That means there are newly available funds to upgrade amss-transit facilities. Singapore did improve its bus service, offsetting most of the cost through ALS sticker fees. The city is now considering a subway system, though it couldn't be in operation until the early 1980s.

An area licensing scheme in any U.S. city would trigger a predictable howl to protest from parking interests and many of the affected auto commuters. There'd be no way to prevent the parking-lot owners' protest, but a city govenment could offer some compelling benefits to auto commuters: much less congested city streets on which to drive to work, in car pools, or alone if they chose to pay the fee, or improved bus facilities if they decided to switch to mass transit.

Experience shows that trying to reduce traffic congestion by simply charging auto users, without some benefit in return, generates too much opposition. San Francisco, for example, imposed a parking surcharge of 25 per cent but was forced to retreat to 10 per cent in the face of public protest. Almost universal opposition met the 1973 suggestion of the Environmental Protection Agency that cities with severe air pollution impose heavy parking surcharges.

Nothing that "people commuting singly in cars is a symbol of profligate waste," former U.S. Transportation Secretary William Coleman recommends experimentation with a Singapore-like system in the United States "to increase vechicle occupancy, reduce congestion, enhance mobility and improve transportation in general."

But an absolute prerequisite, Coleman says, is that a city must have a first-rate public-transportation system in plade: buses or subways or a combination of the two. Concurrently, he says, a city should actively encourage alternative forms of transportatkon, incluging car-pooling, and shared taxis.

Transportation experts say an area licensing scheme is really just a form of user fee - an increasingly polular concept. Examples are peak charges for telephone calls, special taxing districts for areas that receive special services from a county or metropolitan area wide government, and the proposals to impose higher charges for electricity used dutring hours of highest demand.

Auto commuters rarely recognize teh immense cost their presence on clogged streets presents for the society at large: air and noise pollution, traffic hazards, reduced economic activity and immense waste of increasingly scarce petroleum. An area licensing plan backers say, simply brings them face to face with the costs they are imposing on others.

No one can tell whether an area licensing approach would actually work in the United State until it's tried. Americans' love affair with their autos is so deep that sky-high fees might have to be imposed to achieve substantial traffic reduction.

But the Transportation Department remains willing to underwrite some of the costs if it receives a reasonable proposal for a U.S. city willing to take the plunge with a pilot program.