A couple of years ago television station KING conducted a nonscientific experiment to measure the patience of Seattle motorists. It sent a driver into city traffic with instructions to provoke hornblowing.

When the driver found himself first in line at a red light he purposely stayed put after the light changed to green. It took 10 seconds for the first horn to honk.

By the standards of most big cities, where honking usually accompanies rather than follows the light change, 10 seconds would represent a veritable eternity. But a blowing horn is rarely heard in Seattle.

The relative absence of honking horns and other excessive noise in public places reflects this city's success in maintaining quiet and civility as it races toward becoming a major urban center.

Seattle is a city of half a million people, with double that population in the suburbs. Its downtown section boasts an impressive skyline that will grow more so with the construction, announced last week, of a 75-story office building.

And while it is starting to rival San Francisco as a scenic and cosmopolitan urban center, it also is saddled with the familiar ills of big cities: worsening traffice congestion, a nothing-to-brag-about crime record, problems in the schools, less-than-ideal race relations, pockets of poverty, insufficient low-and moderate-income housing, and enough anxiety to challenge San Francisco's high suicide rate.

But in the face of all this is quietude, much of which can be attributed to an agressive campaign by the city to suppress noise. Armed with a 3-year-old noise abatement ordinance, considered by experts to be one of the toughest and most vigorously enforced in the nation, the city in the last year has:

Banished outdoor rock concerts from the Seattle Center. The action was triggered by a concert last summer that drew hundreds of complaints from nearby residents and fines for the concert's promoters. The school system, which sponsored the concert series, recently announced that no more would be permitted unless performers agreed to stringent sound-level restrictions which, according to one official, no self-respecting rock group would accept.

Forced a large dairy to install new and quieter refrigeration units on its fleet of delivery trucks. Neighbors had complained that the all-night idling of the trucks kept them awake.

Required owners of most heat pumps to enclose them in sound-muffling cases to spare neighbors the noise generated by the energy-saving devices.

Blocked the federal government's National Oceanographic and Atmospheric Administration from night dredging on Lake Washington, where the agency was developing a new facility.

Seattle's noise abatement program reaches potential as well as actual noisemakers. Plans for new high-rise buildings are reviewed by the city to determine whether construction would result in a "sound canyon" that would create impermissible noise levels. If so, the building must be redesigned.

But Seattle apparently owes its quiet as much as to the values held by its residents as to its laws. Many other cities officially prohibit honking except to warn of danger. It works here, says Curt Horner, Seattle's noise abatement coordinator, because , "The people themselves have more awareness of noise. They value their quiet."

Dr. William Womack, head of the Division of Community Psychiatry at the University of Washington's Medical School, became aware of the absence of horn-blowing shortly after he arrived here in 1961 from his native Lynchburg, Va. He believes that it is more than courtesy that restrains the Seattle driver.

"It has more to do with the fact that noise is jarring and disruptive of one's environmental space," Womack said. "If you're going to get a nasty retort from anyone in this city, blowing your horn at a light is the way to do it."

Both Seattle's government and its private sector have taken the trouble to promote tranquility. The city, for instance, is dotted with parks and trails that allow people to jog, bike or walk in near solitude.

Commercially, the phenomenon is exemplified by an annual discount ski sale, which this year drew more than 23,000 persons to the Seattle Center's Exhibition Hall. Osborn & Ulland, the firm that held the sale, avoided long and frustrating waits for its customers by giving them an admission number on arrival, allowing them to calculate the approximate time they would be admitted. It gave them the freedom to lunch, tour the center and show up three hours later for a relatively short wait.

Yosh Nakagawa, president of Osborn & Ulland and something of a philosopher about Seattle, said he thinks that Seattle's tranquility results from many factors. He said it may have something to do with the water, the hills and the fir trees that are everywhere in and around Seattle.

"For most of us, within 10 or 15 minutes we're home, and it looks like we're in the middle of the country," he said. "It takes the biting edge off a lot of the anxiety from urban tensions. Sure, there's traffice congestion, but you know you can get out of it. It's not prolonged. In Los Angeles, you never get out."

If Seattle residents ever forget they are living on the edge of the frontier, they can be reminded quickly by something familiar as the weather forcast carried by the telephone company. It comes accompanied by public-service messages, such as a recent one urging motorists driving along the coast to report to the state patrol any beached whales or seal lions.