Denver's experimental "license-plate lottery" came to an end under smoggy skies today with health officials expressing cautious optimism that the voluntary program might have helped reduce auto traffic and thus allowed the area to meet federal clean-air standards.

For the past eight weeks, drivers in this seriously polluted city and five surrounding counties have been asked to leave their cars at home one day a week. Cars with a license number ending in 0 or 1 were not to be used on Mondays, those ending with 2 or 3 on Tuesday, and so on.

Initial assessments reported that the innovative campaign was a quasi-success.

"We did a good job of spreading public awareness of what we wanted," said Ann O'Grady of the Colorado Health Department. She said surveys show 95 percent of area drivers knew about the campaign and 88 percent approved of it.

Unfortunately, many seemed to have approved of the plan only for the other guy. Only 5 percent of the drivers surveyed said they honored their no-drive days; another 15 percent said they eliminated some auto trips.

Local newspapers and television stations had a field day tracking down governmental luminaries who were driving on the day their number was up. The Denver Post last week counted 60 cars in the state legislators' private parking lot on days they were supposed to be left at home.

Nonetheless, even small participation rates made a difference. The 5 percent who complied with the rules took 12,000 cars off the streets here each weekday.

The most encouraging news was that many people evidently did respond on the days when weather conditions created the worst pollution hazards.

"We had 51 percent of our drivers who said they cut back driving on the high-pollution days," said James Lents, who heads the state's air pollution control program. "For a first-year program, that's not terrible."

Denver, once a haven for people seeking clean air and crystalline views of the mighty Rockies rising west of town, has been plagued by a "brown cloud" of particulates and high levels of carbon monoxide from automotive emissions.

This city had more "unhealthy air" alerts last year than Los Angeles, the fabled capital of urban smog.

Unlike most American cities, which have to deal with thermal inversions -- air patterns that hold pollutants in place over downtown -- in summertime, Denver gets its worst air pollution in late fall and winter, when cold air coming off the mountains locks in polluted warmer air swirling over the city.

The city has had a running battle with the Environmental Protection Agency over the best way to achieve the 15 percent reduction in auto traffic that will be required to meet federal air standards by the 1987 deadline. If Denver fails, the region could forfeit tens of millions of dollars in federal highway and sewer-plant construction grants.

The no-drive campaign, touted in advertisements featuring Mayor Federico Pena jogging to work and Gov. Richard D. Lamm (D) riding a bike, got off to a rocky start.

A local columnist, Woody Paige, announced after one day's compliance that he "felt naked and vulnerable all day without a car."

"No one I talk to is willing to sacrifice," Paige wrote. "It's not worth the time and effort."

The campaign also had to cope with plummeting gasoline prices, which presumably encourage driving, and a relatively mild December that saw only one big snowfall, and that only about six inches -- hardly enough to deter the intrepid Colorado driver.

Lents, of the Health Department, said it is too early to draw conclusions about the effort.

"I can show that our air quality is better than it was in the November-January period in the late 1970s," he said. "But I can't pinpoint a reason. New cars are cleaner than old ones, we have an emissions inspection requirement th (National Caucus of Labor Committees photo) those things are part of it, and the no-drive program may be part, too."