This is a city where pedestrians blithely stroll in the middle of busy streets, motorists park on crowded sidewalks, and motorcyclists roar the wrong direction down one-way alleys, scattering unsuspecting sightseers like autumn leaves.

During the Christmas season, holiday shoppers raise the level of random chaos, especially in the city's historic center, a kind of Bermuda Triangle of jostling crowds and runaway vehicles. Enter at your own risk.

This year, City Hall has decided to try to reduce the frenzy by banning automobile and motorcycle traffic for one month, beginning today, from the fashionable central area known as the Trident. The district is framed by three main streets laid out during the days of the Roman Empire and includes renowned tourist landmarks: the picturesque Piazza del Popolo and the Spanish Steps, as well as Via dei Condotti, Rome's most upscale shopping street, and the Via del Corso, one of its busiest commercial thoroughfares.

At issue is a problem vexing many municipalities in Italy: how to promote livability and maintain the splendor of old city centers in the face of burgeoning vehicle and tourist traffic. Florence has long banned automobiles from the fragile Renaissance downtown and toyed with the idea of charging admission to the city.

Venice has grappled with its peculiar problem of reducing boat traffic on its canals because private vessels kick up wakes that damage the foundation of island palazzi. Venice has also tried to encourage tourists to visit in off-peak months by instituting a reservations-only pass to enter museums, ride ferries and use public toilets. Naples has campaigned long and hard to clear its streets of itinerant salespeople, to no avail.

Several Italian cities hold periodic car-free Sundays in their downtowns, but Rome's Christmas plans are the most ambitious effort to clear the streets, and presumably the air, during a busy time. The streets will be closed to motor traffic, except buses and taxis and vehicles belonging to residents who have garage space, between 10 a.m. and 8 p.m. "An historic decision," said Mayor Walter Veltroni.

But some like it chaotic. Trident residents expressed concern that they will be prisoners in their homes. Shopkeepers groused that regular customers will be driven off to suburban shopping malls. Wholesalers wondered how they were going to deliver their goods. . Motorcyclists suspected a plot to drive them off the streets forever.

"People don't see now how to come in a car; imagine coming by taxi or on foot," said Oswaldo Cocozza, an antique dealer on Via Margutta.

"It's a wrong decision at the wrong time and in the wrong manner," said Gianni Battisoni, president of the Via Condotti Merchants Association. "This kind of experiment exclusively creates dissatisfaction."

Riccardo Matesich complained that Rome lacks sufficient public transportation and places to park motorcycles. "Traveling on motorcycle is not a pleasure in Rome, it's a necessity," he said.

A few residents, plus environmentalists, voiced agreement with the vehicle ban. Film director Luigi Magni was quoted in La Repubblica newspaper as saying, "It was time someone did something, even at the cost of appearing tyrannical. It's a courageous gesture."

In Italy, sweeping rules don't necessarily apply to all, and several Trident area residents expressed suspicions that the cars of high-ranking municipal and central government officials will be exempt. Their cars have blue lights mounted on the roof that permit them to motor in bus lanes off-limits to other drivers. But the police have promised to ban even the bigwigs' cars.

Efforts to bring order to Rome's core have been slow but methodical in recent years. Before Veltroni, the administration of Francesco Rutelli ordered municipal workers to mark street parking areas with blue lines, set up meters and regularly ticket violators. Still, double parking is a Roman specialty, and many streets are clogged by cars that protrude from tight spaces.

Some storeowners weary of having their front doors blocked by illegally parked cars put planters out front to obstruct them. This has created impromptu gardens on the city's traditionally barren, stone streets.

Some Romans say the city is invasata, a word that, while seemingly referring to potted plants, literally means driven mad.

Residents enjoy a November day without vehicles at Fori Imperiali Street in Rome, with the Colosseum in the background. The city is banning most cars, trucks and motorbikes from the historic district for one month.