SEATTLE - More than 30 years after Congress set a goal of clearing the pollution-caused haze that obscures scenic vistas at some of America's wildest and most famous natural places, progress is still slow in coming.

Saturday marks the deadline for the U.S. Environmental Protection Agency to approve most state plans aimed at curbing pollution from coal-fired power plants and industrial sources to improve visibility at 156 national parks and wilderness areas such as Shenandoah, Mount Rainier and the Grand Canyon.

The agency hasn't formally approved any state plans - or come up with its own, as required, and won't do so by the deadline.

"We will not have final federal plans in place by Jan. 15," the agency said in an e-mail late Friday. The agency said it has proposed partial approval of Idaho's plan, a partial federal plan for New Mexico and a federal plan for the Four Corners area on tribal land.

The agency added that "there is progress in every state toward visibility improvements, reductions in harmful emissions and the development of state plans."

"Here's a program intended to clean up skies of the nation's most pristine areas. It has been pushed aside for too long and must be made a top-tier priority," said Stephanie Kodish, attorney for the non-profit National Parks Conservation Association. The group plans next week to file a notice of intent to sue the EPA for missing the regulatory deadline.

Nearly three-quarters of states failed to meet an initial 2007 deadline to submit plans requiring decades-old facilities that contribute to haze at parks to update old equipment. So far, only 34 states have done so.

Until states file plans and the EPA approves them, companies aren't obligated to make changes under the haze rule. The EPA, however, says other clean air rules have provisions to protect parks and wilderness areas.

We "are working with the other states to get their plans submitted and approved as quickly as possible," the EPA e-mailed in response to AP questions. The EPA says it is taking the time to ensure strong plans are in place.

In Oklahoma, for example, the EPA is likely to reject a proposal, state officials say, after the state determined it wasn't cost-effective to require six coal-fired units there to install scrubbers. The EPA says such devices would cut sulfur dioxide by one-third.

"We believe that our plan makes sense for Oklahoma," said Skylar McElhaney, a spokeswoman with the state Department of Environmental Quality.

The regional haze results from sulfates and nitrates from coal-fired power plants and industrial boilers, as well as automobiles, carbon from fires, soot and windblown dust. The high cost of controlling emissions, legal battles, the complexity of rules, industry resistance and competing clean air rules have slowed progress in clearing it.

Haze-causing pollution continues to obscure scenic vistas that draw millions of visitors to parks and wilderness areas throughout the country. In eastern parks, average visibility has dropped from 90 miles to between 15 and 25 miles, while visual range in the West has been reduced from 140 miles to between 35 and 90 miles.

The 1977 Clean Air Act established a national goal to restore visibility in protected areas to conditions that would exist naturally, without pollution.

"When you think of national parks, you think of clean and clear air," said John Bunyak, policy chief of the National Park Service air resources division. "If you load up the kids in the family van and drive thousands of miles to the Grand Canyon and can't see the bottom of the canyon, that to me is a problem."

Reducing pollutants to improve visibility also can yield public health benefits, the EPA said. Fine particles that cause haze are linked to serious health problems, such as aggravated asthma, heart attacks and premature death.

The NPCA, the National Park Service, U.S. Forest Service and other groups have pushed states to consider the tough pollution controls such as scrubbers or technology that works like a car's catalytic converter to filter nitrogen oxides.

Installing such devices, however, costs hundreds of millions of dollars, and industry officials say it would lead to skyrocketing utility rates and cripple businesses that are economic drivers in many states. Companies say they're trying to balance improving visibility while ensuring energy reliability and protecting customers from huge rate hikes.

Even some states have concluded it's too expensive to require for some facilities, preferring alternatives such as low-sulfur coal.

"It's understandable that states are having a hard time meeting EPA demands when doing so comes at great costs to consumers," said Paul Seby, an attorney in Denver, who represents coal producers and power companies. The EPA is requiring more of the states than is allowed under the haze rule, he said.

The rule "targets the oldest and the dirtiest coal plants," said Jeremy Nichols, energy program director for WildEarth Guardians. "We have the technology to do better."

By June, the EPA is under a court-deadline to approve state plans - or come up with its own - for California, Colorado, Idaho, New Mexico, North Dakota, Oklahoma, and Oregon, after the group sued.

Park and forest officials, in comments to states, have questioned whether some overestimated the costs of installing pollution devices and whether their plans make enough progress. Haze over Big Bend National Park in Texas or Voyageurs National Park in Minnesota, for example, wouldn't be eliminated for more than a century.

Park and forest officials told Washington state last summer that its plan worsens air quality at North Cascades National Park and Glacier Peak Wilderness. The state's latest analysis, however, disputes that based on updated modeling.

In Oregon, faced with $500 million in retrofits proposed, Portland General Electric Co. has proposed shutting down the state's only coal-fired power plant in Boardman, Ore. by 2020. The company has struck a balance between reducing pollution and ensuring energy reliability, said Dave Robertson, PGE vice president for public policy.

At Shenandoah National Park in Virginia, visitors can only see on average about 12 miles, or one-tenth what it should be under natural conditions.

"Historically, our claim to fame was to see the Washington Monument," located 80 miles away, from the park's Skyline Drive, said Jim Schaberl, park air quality manager. "It's a rare occasion, generally during the winter, when people can see the monument from the drive."