Farmers' markets are returning to the city at what seems the rate they were driven out 10 and 20 years ago.

They bring better health both for people and the city, and symbolize towards cities and life.

Faneuil Hall Marketplace in Boston is only the most dramatic example. It's third and final phase was completed with much fanfare a few days ago. It attracts well over 35,000 people a day.

At a cost of some $30 million for the restoration of the historic Quincy market halls, that makes it easily the country's most successful urban renewal project.

And while Faneuil Hall Marketplace also offers fashionable stores, restaurants and offices - it has some of the qualities of an ancient Greek agora - the produce and fish stands are surely its essence. They animate the drama of the place with its aroma of fish, fruit and produce, its backdrop of great historic architecture, architect Ben Thompson's stagecraft and the choreography of a medley of people, plain and fancy.

There are no national statistics yet, but hundreds of farmers' markets opened or re-opened in the past few years. Some are no bigger than a cluster of three or four farm trucks doing business a few hours a week on a church parking lot.

The U.S. Department of Agriculture, though it welcomes the trend, does not know just how important the trend is to farmers and the farm economy. But with a thousand farmers a week leaving their farms for other jobs and half the nation's farms lost between 1950 and 1975, anything that keeps them on the farm is important.

For the past three years, Congress has allocated about $1.5 million a year to assist this "farmer to consumer direct marketing."

In addition, several organizations around the country are working to encourage direct marketing to help keep young farmers on the land, foster town and country cooperation, arrest the monopoly of the food chains and provide more nutritious food for city folk.

One of these organizations, the Agricultural Marketing Project, which operates in Mississippi, Tennessee and Alabama, conducts information campaigns about nutrition, negotiates sensible sanitation regulations for markets with the authorities, and employs agriculture students to persuade church and neighborhood groups to make its parking lots and other open space available for farmers. In just a few months, AMP managed to set up "food fairs" in 26 southern cities.

Another similar and similarly successful "direct marketing" program operates in New York City and is called "Greenspace."

On the average, produce sold directly by a farmer costs half as much as produce checked out by computer. The farmer, according to AMP, is paid 16 percent more than the wholesaler will pay him.

In addition to a better price, the consumer gets better food. The dangers of junk food and over-processed foods are increasingly apparent. Fresh, locally grown foods look better, taste better and are more nutritious than the packaged miracles of modern food technology.

Nor is home-grown food only a fad of the idle rich or the health nuts. Some social welfare agencies are beginning to teach the poor how to get more nutrition for less money by cooking, rather than merely heating "convenience" foods.

But the return of the farmers' markets is no more only a matter of health than the closing of farmers' markets some decades ago. Then as now, the presence of farmers in the city is a matter of politics, which may be defined as a combination of changing conviction and changing economics.

When the markets were closed and driven out of town, the authorities claimed inefficiency and health hazards. The claim was and is mostly ludicrous. What is a speck of earth on a tomato compared with the coloring additives and other chemistry applied to supermarket food? Nevertheless, some zealous health inspectors still make it a sport to hassle farm women with sanitary regulations they would not apply to hospitals, let alone expensive restaurants.

What "inefficiency" really meant was that city officials thought supermarkets would bring higher tax revenues, which indeed they do - out in the suburbs. Sanitation was more often than not the code word for land grab - land for parking lots and highrise buildings. It was not always as sinister as it sounds in retrospect. Mayors, city councils and many citizens sincerely believed that more parking, higher buildings and labor-saving supermarkets, being "modern," would bring progress.

The rebellion against this kind of progress started 10 years ago when the Seattle city council approved a plan to destroy the famous and fabulous Pike Place Market in the name of urban renewal - a parking garage, a hotel and apartment towers.

True, Pike Market was in decline at the time. World War II hysteria had driven Japanese truck farmers from their land. Suburbanization and traffic congestion discouraged other farmers. The market's 240 stands had dwindled to 56.

But most Seattle citizens wanted their ailing market cured, not killed. They certainly wanted no urban renewal. The issue was put to referendum, and saving the market won the approval of Seattle voters in November 1971. Today it is thriving, not only as a tourist attraction, but as an assertion of Seattle's liveliness and urbanity.

Seattle changed the tide. The renovation of the Lancaster market in the center of the Pennsylvania Dutch farming country reinforced it. Planners also began to look at Baltimore, the only city in the country, according the city planner Ann Satterthwaite, which has kept its system of eight markets in downtown neighborhoods.

The planners found that far from holding up progress, the markets in Seattle, Lancaster, Baltimore and other places helped to keep the city's body and soul together.

It is not only, as Satterthwaite says, that what seemed blighted, outdated and inefficient in the 1960s is suddenly popular and even chic in the '70s.

Economics now demands keeping people on the land and promoting labor-intensive businesses rather than automating everything, including automatic increases in the number of the unemployed.

We nowdemand not efficiency so much as amenity: the satisfaction of personal contact with the people who sell us our food, the sensory experience of selecting your tomato or peach, of testing its ripeness and sniffing its aroma.

A farmers' market makes shopping an experience that brings us a little closer to nature - to sunshine that ripens fruits and vegetable, the sea that gives us fish, the barnyard our eggs come from - the seasons and the weather.

Markets are a manifestation of community - and of our humanity.