For most of the world, this city's Copacabana district summons up an image of a dazzling blue bay, a white beach and a crescent of elegant hotels and apartment houses laced with tropical color and the rhythms of the samba.

But for the cariocas, the people of Rio, Copacabana has increasingly come to mean an overcrowded, overbuilt urban wedge of high pollution, questionable sanitation, rampant crime and chaotic traffic.

Each month, the shantytowns on the edges spread a little further over its verdant hillsides, and each day, hundreds of buses and thousands of cars on its narrow streets flirt with gridlock.

Enter Jaime Lerner, 45, an urban architect who is asking Copacabana's residents to imagine a partial solution to the trouble: the "surface metro."

Under Lerner's plan, hundreds of buses, with their roar and clutter, would be eliminated from the neighborhood and replaced by a sleek, fleet of jointed, snake-like vehicles gliding to pick up passengers waiting in silvery tubes. Cluttered streets would be divided with rows of yellow stones to mark room for the new buses.

The scheme may sound improbable, but Lerner, the director of Eio's Project 2000, says his futuristic transportation is practical in debt-stricken Brazil. In that sense, he adds, it is a model of how the country's vast cities can find solutions to their growth problems.

Lerner says the surface metro should be operating in Copacabana by the middle of next year, reducing the traffic passing through the district of some two square miles from 500 buses per hour to 100 virtually overnight.

"This is the kind of answer we have to look for," he said in his downtown office, hunched over metro models. "For the next 10 or 15 years, we are not going to have a lot of resources in Brazil to solve our urban problems. So we have to make up with creativity."

Lerner was contracted a year ago by Rio state Gov. Leonel Brizola to do just this kind of thinking. The former mayor of the rapidly growing city of Curitiba in Parana state, Lerner has made a career of inventing modest but workable solutions for overcrowded, underserviced cities -- from futuristic transportation systems to renovations of business districts and slums.

Assisted by a staff of 40, Lerner now faces the task of designing a plan for Rio, with its 7 million inhabitants, that will prepare it for the next century. "The idea is to have a vision of the future tied to the present," he said. "Because if we don't convert our ideas into something specific, what we produce will end up being another stack of paper."

Rio has already become a city where fundamental reform cannot wait for another decade. Once the glittering jewel of a poor tropical country, with a spectacular natural setting and extravagant nightlife, Rio is now monument both to Brazil's rapid industrialization and the havoc it can cause.

Stretched in a long, narrow arc between the South Atlantic and rolling green mountains, Rio has been clogged with factories, highways and high rises in recent years and polluted by fumes and liquid wastes. Air pilots call its regular smog cover "the cloud of death."

The water lapping the beach in Copacabana, meanwhile, has been labeled "unsuitable for bathing" by a local environmental foundation.

Massive migration of poor laborers from the countryside has increased Rio's population by an average of 130,000 annually since the late 1970s, according to government figures. Meanwhile, annual spending on services by the city's administration has fallen by 15 percent in six years.

Illegal settlements of squatter shacks have more than doubled in number since 1960. Officials say that 377 such shantytowns now cover 60 of the 180 ridges and mountainsides in Rio and hold a population of up to 1 million.

Four years of economic recession have turned many of the city's problems from bad to critical. With unemployment running high, a wave of supermarket sackings by mobs stunned Rio last year. This year, robbery and assault rates are up by 40 percent, prompting Brizola to declare that Rio had matched New York in crime.

"The world knows Rio for its natural beauty . . . but the economic crisis, violence and the tensions of modern life have tarnished the image," the morning newspaper Jornal do Brasil recently commented. "Some authority needs to love this city."

Lerner, who would like to be that authority, blames much of the trouble on Rio's style of development in the last 30 years. "We suffered what happened to a lot of large, developing cities," he said.

"Our investment went into the automobile and highways, and we ended up importing a reality from developed countries that has nothing to do with us. We had 400 kilometers of street car lines 40 years ago. Now we have almost none. No one ever stopped to think what it all was for."

With such an analysis, it was only logical that Lerner begin by seeking to reorganize Rio's chaotic public transportation, which includes suburban trains, a subway and coastal boats. But at the heart of the system are 8,000 buses transporting some 8 million passengers daily -- the largest urban bus fleet, Lerner said, in the western world.

The architect's solution is unprecedented in a large city, but remarkably economical. Hundreds of traditional buses are to be replaced by long "articulated" buses, much like those in Washington with the accordian-like joints between two central carriages. The spare seating configuration would allow them to carry 200 passengers.

These new vehicles, made in Brazil for about $100,000 a piece, will use exclusive, 12-foot lanes on city streets and highways and stop every 550 yards at specially designed tubes mounted on sidewalks.

Rather than hailing a bus from the street and paying the driver, passengers will pay fares on entering the cylindrical stations and line up inside, boarding the buses when their automatic doors align with the tube and woosh open in the fashion of a subway train.

With buses arriving at stops every three minutes, Lerner estimates that the 100 vehicles initiating the system in Copacabana could transport up to 15,000 people an hour, approximating the capacity of a subway system at a fraction of the cost. "This is not just a poor man's system," he said. "It would make sense anywhere because it's efficient."

The surface metro is just the beginning of Lerner's plans. He would also like to liven the business district, deserted at night, with thousands of permanent residents, and install a long-distance monorail on the outskirts for rapid travel.