ONDON, Feb. 16 — After endless debates, countless protests, months of planning and an expenditure of some $310 million, London's daring scheme to reduce the number of cars clogging its increasingly gridlocked streets is finally to take effect. As of 7 a.m. Monday, motorists wanting to drive into central London during weekday business hours will have to pay £5, or nearly $8, for the privilege.

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The city's subway-riding mayor, Ken Livingstone, has staked his political reputation on the success of his program, saying he expects it to cut traffic by 10 to 15 percent and lead to a 25 percent reduction in traffic delays. But with many London workers and residents still passionately opposed to the plan, it will not be clear for some time how successful Mr. Livingstone will be in persuading people either to stop driving or to start paying.

Other cities, most notably Singapore and Oslo, have their own methods of charging drivers for bringing their cars into town. But no program has ever before been tried on this scale in a city as big as London and with such complicated traffic patterns.

London's project is being carefully watched in cities facing their own traffic problems on both sides of the Atlantic. If it proves successful, it is likely to replicated in urban centers across Britain.

But it is surrounded by huge question marks, starting with the technology: in the first, unfortunate glitch, 45 people have already been fined £120, or almost $200, for failing to pay the fee — even before the charges have begun.

Early on, the mayor ruled out using "smart cards" similar to the E-ZPass system in use on many bridges and toll roads in the United States, arguing that such a system would be too cumbersome and would prove too unfamiliar to London's drivers. Instead, London's plan relies on a network of video cameras similar to the speed cameras already installed on roads across Britain.

Under the plan, some 700 such cameras distributed throughout the so-called congestion zone, an eight-square-mile area in the center of London, will take repeated pictures of the license plate of any car that drives through between the hours of 7 a.m. and 6:30 p.m., except on weekends and holidays. The images will be fed into computers that will then match the license plates of those cars photographed against a list of drivers who have paid for the trip.

Trips into the zone — whether or not the driver gets out of the car, and regardless of how long the car is actually in the congestion area — cost £5 a day. Motorists can pay in advance, either on line, over the telephone, or at specially installed machines at newspaper shops, food stores and gas stations across London. Failure to pay by 10 p.m. on the day the trip is made doubles the fee to £10.

After midnight, the £10, or about $15, instantly increases to £40 for the next two weeks, and then to £80 — more than $120 — for the two weeks after that. Drivers who still fail to pay within a month will be charged the full £120, and those who ignore three such fines face having their cars clamped or towed away.

There has been much discussion of drivers refusing to pay, or of people deliberately obscuring their license plates or affixing fake plates in an illegal effort to avoid detection. But it seems that shirkers will find it hard to evade the law indefinitely.
"Anyone who doesn't pay," a mayoral spokesman said recently, "will find that there are many ways we can pursue you."

Some vehicles, including taxi cabs and cars registered to disabled drivers, are exempt from the charge. Many motorists have pleaded hardship nevertheless, but to no avail. Numerous groups, including actors in the West End; meat-market workers in the East End; and teachers and health-care workers with jobs across the city, have said that the charges will impose unfair burdens on them and might make it impossible for them to work in London at all.

In addition, people who live near the outer borders of the congestion zone are worried that drivers will flood their neighborhood streets in their attempts to avoid paying the fee. Already, parking charges in areas just outside the zone have risen by a reported 60 percent.

Meanwhile, opponents of the project have threatened to inundate the mayor's telephone payment center with calls in an effort to snarl the lines. On Monday, various groups of protesters are expected to stage anti-charging demonstrations at key points around the charging zone.

There is no question that central London has a huge traffic problem. Some 250,000 cars enter the central zone every workday, moving at an average rush-hour speed of less than 10 miles an hour. The problem has only increased in the last year or two with the introduction of new traffic lights, the widening of some sidewalks and a higher than usual complement of construction projects.

Mayor Livingstone hopes that people who abandon their cars will switch to public transportation, and has pledged to invest the proceeds from the congestion charges — an expected $204 million a year — in the city's buses. But surveys have shown that many drivers would sooner switch to the subway than get on a bus, which will bring its own headaches.

Two major subway lines, the Central Line and the Waterloo and City Lines, were indefinitely closed after an accident last month, leaving tens of thousands of commuters without an easy way to get to work and adding to the general misery underground.

"Underground and rail networks are operating at capacity," Angela Bray, a Conservative member of the London Assembly, wrote in a letter to The Guardian this weekend. "If a traveler actually gets on to a train, he or she can expect conditions so overcrowded that they would breach E.U. laws on transportation of cattle."

Much is riding on the congestion-charge plan, not least Mayor Livingstone's political future. Although he tried to distance himself from his remark soon after he made it, the mayor said last year that he would scrap the charges after two months if the project proved to be a failure. With the next mayoral election scheduled for 2004, he has little breathing room, especially given the high profile of the endeavor.

The two men competing to be the Conservative mayoral candidate in the 2004 election have both made repeal of the congestion project the cornerstone of their campaigns.

"I cannot see how it will work," said Roger Evans, a member of the London Assembly, who is vying for the nomination against Steve Norris, a former Tory Transport Minister. Speaking of Mr. Livingstone, he added, "Ken might even end up scrapping it before we get in."