Dairy herds still roam the hills here and 100-year-old buildings are not uncommon.

Yet fear of congestion in this rapidly growing area 30 miles southeast of San Francisco has prompted the city of Pleasanton to adopt one of the nation's first "traffic management" ordinances.

It requires companies that employ at least 50 people on a single shift to reduce the number of single-occupant automobile trips during peak hours by an average of 30 percent over four years.

Employers may change work hours, encourage or require workers to join car or van pools, or take any other steps they like. But they must reduce single-occupant trips 15 percent in the first year, 25 percent in the second year, 35 percent in the third year and 45 percent by the end of the fourth year.

For now, the program is voluntary. But if goals are not being met at the end of two years, the Pleasanton City Council can shift to a mandatory approach and fine recalcitrant employers up to $250 a day.

A task force made up almost entirely of representatives of private industry and the business parks was established to monitor the ordinance. Only if the task force is unable for two years to persuade an employer to comply with the ordinance would the case go to the city council for a hearing and possible penalties.

The ordinance approved by the council in October grew out of a 300-member citizens' committee's 1980 recommendation that companies moving into the business parks, as well as those already in Pleasanton, be required to adopt policies that would reduce the number of peak-hour auto trips.

"The city has taken some pretty dramatic and far-reaching steps," Gail Gilpin, the new Pleasanton transportation coordinator, said. "They're obviously putting the quality of life above growth."

This attractive bit of suburbia at the far eastern end of Alameda County has much in common with the burgeoning suburbs around Washington, D.C., Los Angeles, Dallas, Houston, Phoenix and other American cities.

Many companies are moving out of the central city and into suburban business or office parks because land costs and office rentals are cheaper and workers are more plentiful. The white-collar families that fled to the suburbs in the 1960s and '70s provide a large employment pool.

"Combined with shopping malls, recreational theme parks and other large-scale land uses, outlying office parks are unquestionably reshaping the landscapes of suburban America," Robert Cervero of the University of California at Berkeley said.

Many of the new business parks are located in areas with little or no public transit, so workers crowd into their cars, creating the kinds of traffic jams Pleasanton hopes to avoid with its new ordinance.

"Traffic congestion is truly monumental in some areas," said Kenneth Orski, a Washington transportation consultant. "This may well be the transportation problem of the late 1980s and early 1990s."

Increasingly, cities and counties are insisting that developers pay special fees for transportation improvements before they may proceed with their projects.

A new ordinance in Orange County in southern California requires developers to pay special fees on all new construction in three transit corridors in which freeways are to be built. The "corridor fees" are expected to yield about $630 million, more than 60 percent of the total cost of building the three freeways.

The Los Angeles city planning staff is considering levying a one-time "development fee" of $800 for each automobile trip generated by construction in Westwood on the western side of the city.

Several experts at a recent University of California conference said mobility could be better preserved in the new suburban business parks by building them in stages and constructing housing nearby.

There was general agreement that mass transit systems, especially fixed-rail lines, do little to relieve congestion in low-density suburban areas. In some cases, they said, the systems aggravate the problem.

According to Orski, studies show that less than 5 percent of the employes in buildings that have sprung up near suburban stations of two major rapid transit systems use the subway to get to their jobs.