DENVER - Facing the threat of federal sanctions, Colorado health officials are considering tougher air pollution controls statewide on the expanding oil and gas industry.

Regulators say emissions from natural gas wells in Weld County and other parts of eastern Colorado are growing at a higher-than-expected rate, jeopardizing an ozone-reduction plan preventing the state from running afoul of the federal government.

"We've gotten a handle on most of the pollution sources, except oil and gas," said Mike Silverstein, manager of planning and policy for the state air pollution control division.

Industry officials say the state health department's own figures show that natural gas exploration and production in northeastern Colorado emits just a small portion of the smog-causing ozone compared to vehicles.

Adding more pollution-control equipment would cost energy companies tens of millions of dollars for what might be negligible improvement, said Ken Wonstolen, senior vice president and general counsel for the Colorado Oil and Gas Association, a trade group.

State regulators are concerned about fulfilling an agreement that exempts Colorado from expensive and burdensome federal regulations if it reduces levels of smog-causing ozone in Denver and other counties along the Front Range by next year.

A looming problem, regulators say, is that ozone levels from gas production are projected to be much higher than those in the agreement, called the Early Action Compact. Weld County, among nine counties where the Environmental Protection Agency says ozone is too high, is one of Colorado's largest gas-producing areas.

Ozone is created when industrial pollution and car exhaust interact with sunlight on bright, sunny days. It poses significant health risks, especially for young children and people with respiratory problems.

Silverstein said air quality control staffers are working on a proposal that would mandate lower emissions from oil and gas producers in northeastern Colorado by next year and phase in similar reductions for wells in other parts of the state, including western Colorado.

The plan is to submit the proposal to the Air Quality Control Commission in August and hold a public hearing in November.

Regulators are concerned about the so-called "flash emissions," releases that occur when gas and other liquids are taken out of the ground or stored in tanks. The agreement with the EPA envisioned those emissions would total 146 tons a day by 2007.

Silverstein said new projections, based on the state's record gas drilling rates, show the total reaching 200 tons a day this year and 235 tons next year.

During a meeting Thursday at the Colorado Department of Public Health and the Environment, regulators discussed proposed regulations. Industry officials questioned the proposal based on recent results from a monitoring station that showed vehicles accounted for 10.5 parts per billion of pollution compared with 0.5 parts per billion from gas wells.

Wonstolen of the Colorado Oil and Gas Association said getting more "old klunkers" off the road would likely do more to cut ozone pollution than targeting gas production.

Silverstein, though, said emissions from vehicles and other sources are decreasing but increasing from gas wells.

After years of struggling with high pollution levels, the Denver area was declared in compliance with all federal clean-air standards in 2002.

Two years later, the EPA said the air in a nine-county swath along the Front Range exceeded federal ozone levels. The EPA agreed to put off declaring the region as a "non-attainment area," or out of compliance, in exchange for the state's plan to reduce ozone by 2007.