A test run costing 3.8 billion crowns ($485.2 million) starts on Tuesday and will last until July. Stockholmers will vote in September 2006 on whether to make it permanent.

Cameras on gantries have sprung up to record the licence numbers of vehicles, whose owners have to pay when they enter and leave the zone.

Most Swedes take pride in their country's environmentalist credentials, but this time politicians may be out of touch with public opinion in their efforts to impose a tax on traffic.

The charge is part of a political deal to secure the support of the Green Party, the smallest group represented in parliament, for Prime Minister Goran Persson's Social Democrat minority government.

It is being launched despite the fact that Persson's fellow Social Democrats on Stockholm city council pledged not to introduce such a scheme when they fought and won local elections in 2002.

The Greens insist the charge is needed because of the growing volume of traffic. "The alternative is to sit in traffic jams for the next 10 years," said Claes Roxbergh, a Green Party member of parliament and chairman of its traffic committee.

Social Democrat mayor Annika Billstrom has also thrown her weight behind the scheme, hammering home the message that traffic jams cost society between 6 billion and 8 billion crowns a year.

"This is paid by you and me as consumers in shape of higher prices for things like goods and food," she told Reuters.

The charge will be a maximum 60 crowns ($7.50) a day, slightly less than London, the only other European capital with similar fees, which charges eight pounds ($14) a day.

TALK OF THE TOWN

While Stockholm's traffic problems are a far cry from those of bigger cities such as Moscow or London, opinion polls show most Stockholmers agree that the Greens have a point.

However, polls also show they are less convinced that congestion charges are the solution. "I think it is crazy to spend so much money on something that just won't pay off," said Stockholm resident Eva Jeckert.

Christmas parties in the city have resounded to heated arguments about the charge, fuelled by a few glasses of traditional mulled wine.

A recent opinion poll showed that nearly 60 percent of those questioned opposed the charge while about 30 percent were in favour.

The Swedish Automobile Association says it receives calls and letters every day about the new tolls from angry and distressed Stockholmers.

"People just feel completely run over." said Maria Spetz, the association's chief executive.

Newspapers have set up "toll ombudsmen" to address readers' concerns about the charges and one has appealed for suggestions on how best to avoid it.

One Web site has a humorous but illegal solution, offering stickers shaped like number plates bearing the registration of Green Party leader Peter Eriksson's car.

TOUGH FIGHT

Despite the criticism and the opinion polls, advocates of the charge may yet win the day.

Many inner city dwellers do not drive or own a car, partly because of the lack of parking spaces, instead using public transport which is being beefed up ahead of the experiment.

The experience of London, set to double the area covered by its charging system in 2007, also indicates that a defeat for the Stockholm scheme may be far from certain.

Opposition to the charges was widespread in the British capital before their introduction, but three years later polls show Londoners have warmed to the system.

"There was lots of apocalyptic talk before it was introduced about the impact it would have," said Transport for London spokesman Richard Dodd.

"People said things like public transport will not cope, London will become a ghost town, businesses will be driven out and nobody will come to central London to shop any more."

"None of that has turned out to be true."

The Swedish charge aims to cut traffic on the most heavily congested roads by 10-15 percent. In London, which introduced charges in 2001, the toll has cut traffic volume by 18 percent.

The charge is also intended to bring about an overall improvement in the urban environment in Stockholm, particularly air quality.

However, researchers say that seven months may not be enough for the Swedish experiment to show any results and, for now, it is the nay sayers who are being heard most.

"I hate those charges," said Stockholmer Ingrid Ohman. "They're pointless and a waste of money. It would be better to use the money help people fix their teeth."