In an innovative effort to pierce the veil of pollution that drapes this city each winter, Denver this week will begin a new "license-plate lottery" designed to reduce auto traffic in the metropolitan area by 15 percent.
For eight weeks, drivers in six counties covering a 40-mile radius around the city will be asked not to drive their cars one day each week.
The voluntary program -- which could be made mandatory if it doesn't work -- is based on license plates. For cars with a license number ending in 0 or 1, the "No-Drive Day" will be Monday; for those with numbers ending in 2 or 3, it is Tuesday, and so on.
The "No-Drive" drive has been launched with a $200,000 advertising campaign featuring television spots in which Colorado Gov. Richard D. Lamm, cruising along on a bicycle, comes upon Denver Mayor Federico Pena, who is running to work in a sport coat, tie and jogging shorts. "Nice knees, mayor," the governor says.
The state Health Department has committed $500,000 -- about half of it from the federal government -- to administer the campaign. The money will pay for a central car-pool information bureau and research equipment to see whether the voluntary program is working.
Denver is under the gun to find something that will help curb its annual early-winter onslaught of air pollution, which renders the city officially "unhealthy" for two or three days each week. Under the Clean Air Act, the city must reduce carbon monoxide in its atmosphere by 15 percent by 1987 or lose tens of millions of dollars in federal aid.
Even if it does reduce carbon monoxide, the new campaign is expected to have only a minor effect on the city's infamous "brown cloud," an ugly haze that hovers over the city and reduces the once-splendid view of the nearby Rocky Mountains to vague shapes in the distance.
The brown cloud is formed by particulates from industrial smokestacks, wood-burning stoves and other sources.
Unlike most parts of the country, where "thermal inversions" trapping air pollution are a summertime occurrence, Denver gets its worst pollution from November through January. Cold air pouring off the mountains west of the city forms a canopy holding polluted air over the city for days at a time.
Denver officials thought up the voluntary No-Drive campaign two years ago in response to orders from the Environmental Protection Agency that they take strong action to curb carbon monoxide.
At first, the EPA rejected the plan. Then-Administrator Anne M. Burford, who was frequently criticized for laxity in enforcing environmental standards, said a voluntary plan could not work and demanded stiffer action from the city.
But Burford's successor, William D. Ruckelshaus, who has a reputation as a much tougher regulator, decided to let Denver give its voluntary plan a try.
"We think it will work because we all know the alternative," said Dave Farrel, a local Chamber of Commerce official on the campaign's central coordinating committee. "There's every likelihood that we'll have to force people to leave their cars home if they don't do it voluntarily."
All of the city's major employers and many small ones have responded to the challenge.
Shelter America, a local mortgage banker, has bought a fleet of 10-speed bicycles to lend to employes on their "No-Drive" days, as well as a large supply of bus tokens to be awarded in employe lotteries.