On city streets everywhere these days, there's an ongoing struggle between muscles and motors. This takes different forms in different places: in San Francisco, mass protests seem to call for a sort of pedal-power politics; in Paris, Rez Sacharoff finds, protesters are no less determined but much more polite. In an accompanying story, Michael Blanding provides a sketch of the international two wheel revolution. Sacharoff a veteran of San Francisco's Critical Mass bicycle movement, and a writer for YO! (Youth Outlook), reports from Paris. Blanding, a freelance writer who bicycles to and from work, reports from San Francisco.

PARIS -- En route to cop a baguette for me and ma cherie, I am stopped by the sound of horns, shouting, whistles. Some 300 travelers, mounted on various muscle-powered vehicles, are causing chaos like San Francisco's "Critical Mass" bike demos, only in French.

Here, protesters bring traffic to a halt by plopping their bikes down in front of motorists -- whose reactions seem to blend sympathy, amusement and anger. "Calmez vous," one smiling biker tells an indignant driver. "This is the only time of the month that we take the power to be free in the streets -- so stop shouting at us."

I run to a friend's apartment, grab her bike and join the mass -- asking questions along the way. (Try taking notes in a foreign language while going uphill on a broken three-speed.)

The rally, flanked by a small army of cops, is heading north. Just in front of me is a young "rude boy" on old-fashioned roller skates, wearing shades, a tie, and a three-piece suit. To my left is one of the route planners, a boy in his late teens, in a black and white Palestinian scarf.

"We start at the Bastille at 2 p.m. on the first Saturday of the month," he tells me. This is the monument that marks the site of the original rebel street party, in July of 1789, when enraged citizens stormed the prison (the Bastille) freeing prisoners and fueling the Revolution that led to the overthrow of the monarchy and the establishment of the First Republic.

From fellow-riders, I learn that these bike demos have been going on for five years now. One sponsor is "Chiche," a coalition of environmental youth groups. They have issued a list of demands, including more bike routes, non-polluting public transportation and a halt to new road construction. Their pamphlet asks motorists "How can you stay happy when two hours of your day are stolen when your car is blocked in a traffic jam? It's a short life -- too bad you're locked up in the cockpit of a stinking car."

Rides have drawn up to 5,000 participants, one young activist tells me. "People say you can't change the world, but we are trying to do just that."

As with San Francisco's Critical Mass, people come for their own reasons and some simply for the pleasure of the ride.

"This is where I can practice my dance moves," says one limber rollerblader, "without fear of being hit by cars."

Unlike San Francisco's demos, the Parisian "manifs" don't include confrontations with police. The rides are carefully planned, and the route cleared with city officials.

San Francisco's fiercely autonomous riders are not so much petitioning government as engaging in self-government. On the other hand, while the city of Paris can veto proposed routes, it has shown a certain leniency. The number of police accompanying the ride seems ridiculous, but last month's fifth anniversary ride ended in a major road occupation, again more or less sanctioned.

As the ride continues, I follow a young couple skating side by side, pushing a baby buckled snugly into a well-oiled stroller. Dashing around us are kids on day-glow mountain bikes, exulting in the chance to commit traffic violations with no penalty.

Underneath the fun and games is real concern with escalating auto traffic. Exhaust emissions erode centuries-old stone facades, and have been linked to cardiovascular illness and death. Last year, 739 deaths and 33,251 serious injuries in the greater Parisian metropolitan area were attributed to automobile traffic.

The ride slows as we reach our destination, the ancient Pere Lachaise cemetery. A bearded man unties a bundle of kindling and lights a fire in a metal cylinder mounted on his bike's steering column. As the setting sun paints red and orange stripes on the polluted horizon, riders gather in the formerly-busy boulevard to warm wind beaten hands by the fire -- and I realize I've forgotten all about that baguette

SIDEBAR - 405 WORDS

Bike Protests Go Global

By Michael Blanding

While delegates to last month's Kyoto Summit on the climate debated how to shave percentage points off fossil fuel emissions, cyclists took to their bikes in a two-wheeled revolution that is rolling across the glove. In Sydney, Australia, 750 bicyclists took over all eight lanes of the Harbour Bridge -- one of that city's most recognizable landmarks. In Toronto, cyclists donned city uniforms and painted a bike lane across from City Hall. In Lyon, France police on mopeds escorted 50 cyclists through the city center and briefly onto the freeway.

The bikers don't always find police so cooperative. Last summer, over a hundred cyclists were arrested for unlawful assembly and traffic violations In San Francisco. Charges against all but three people have since been dismissed, but there is a new level of tension between police, motorists, and cyclists on the monthly rides. In Sydney, authorities declared the ride an unlawful assembly, and threatened arrests.

But arrests are unlikely to deter cyclists who see their movement as essential to raising awareness about everything from pollution to consumerism.

"As well as being a celebration of cycling, Critical Mass is a protest at the Government's failure to grapple with the appalling air quality situation, global warming and the domination of the City by private cars and heavy trucks," says Sydney's Brent Hoare. "As long as governments keep sitting on their hands and bending over to big oil, coal and the road builders, let's hope CM keeps growing and getting more and more vociferous."

Critical Mass in San Francisco has so far been largely concerned with promoting bike lanes and other facilities for bicyclists, though individual participants have always had their own motivations. Declaring itself an "organized coincidence" rather than an organization as such, Critical Mass has never had leaders, organizational hierarchy or a statement of purpose.

Greenhouse Mass represents a politicization of that movement -- with the Internet helping to coordinate volunteers from various countries. Many cities now have local e-mail lists, and recently a new forum, dubbed "kyoto-climax", surfaced to coordinate international communications.

More than anything else, Critical Mass tries to demonstrate that the city belongs to people and not machines. For those who ride, the bicycle is the ideal symbol for protesting the destruction contained in the combustion engine. And while the car-driving populace might blanch at the idea of unruly cyclists disrupting its evening commute, they aren't likely to go away any time soon.