In the environmentally enlightened age of Earth Day two decades ago, Congress decided that state governments could be trusted to carry out the popular will for clean air.

But the Clean Air Act of 1970, in which states were to "provide for attainment" of air quality standards in their cities, has fallen far short of its goals for ozone and carbon monoxide. The deadline for reducing levels of those dangerous pollutants has been extended twice, and nearly all of the nation's 83 largest metropolitan areas still exceed the standards.

On Tuesday, the Environmental Protection Agency delayed the due date again, dropping the club of economic sanctions in favor of a new plan that critics said contains the same formula for failure as the past 17 years.

Instead of prescribing new pollution controls of the kind being advocated by states, environmentalists and members of Congress, the EPA left responsibility for the cure in the hands of state and local planners. The plan merely stretches out the deadline for meeting the standards -- a grace period of up to eight years for cities seeking to avoid construction bans and up to decades for those hoping to stave off cutoffs in federal highway, sewage treatment and air pollution grants.

Cities unable to meet the standards by 1996 would be forced to halt construction of new polluting industries. But as long as they cut ozone and carbon monoxide levels by 3 percent annually, there will be no further penalty.

EPA Administrator Lee M. Thomas called the plan "tough but reasonable" and defended his decision to continue to rely on states for pollution controls, saying that elected officials "don't want to abdicate responsibility to the federal government."

But critics said Thomas' theory ignores a 17-year history in which the states have failed to implement the politically unpopular programs -- such as auto emission inspections -- needed to curb ozone and carbon monoxide pollution. W. Blakeman Early of the Sierra Club draws a comparison to a sequence in the "Peanuts" cartoon strip in which Lucy every fall holds a football for Charlie Brown, invites him to kick it, then pulls the ball away just as he is about to make contact.

"Lee Thomas is Lucy and the public is Charlie Brown, and Thomas is saying, 'Come on and take another run at kicking it,' " Early said. "I fear the results will be the same as in previous years."

Coincidentally, some of the harshest criticism of the Thomas plan has come from representatives of the most polluted areas, which were certain to have been penalized for failing to meet the latest statutory deadline of Dec. 31.

"This lets everyone off the hook," said Steven Howards, executive director of the Denver Metropolitan Air Quality Council. "It tells cities if you wait long enough, the federal government will back off. Is that the type of message the federal government should be sending when the lives of millions of people are at stake?"

Denver's pollution is so bad that the city is expected to receive a construction ban. But Howards said the 3 percent annual cutbacks required in the Thomas plan to avoid federal grant cutbacks is so lenient that it all but eliminates a useful threat.

"It's apparent that cities all over the country need EPA's prod to institute tough cleanup initiatives," Howards said in a telephone interview. "The threat of federal sanctions is very useful in transmitting to decision-makers the urgency of acting to clean up the air. Given the special interests that lobby against pollution controls and the fact that you're often dealing with controversial changes in life style, you need all the help that you can get."

Not only is a strong federal role sought to help absorb the political heat of pollution controls, but the EPA is looked to for regulations that exceed state authority.

Seven northeastern states jointly criticized the Thomas plan for failing to cut auto emissions further and develop regulations to deal with pollution that crosses into the region from midwestern industries. According to Tom Jorling, commissioner of the New York State Department of Environmental Conservation, "There are some things we can't do by ourselves."

None of Thomas' critics debates the need for more time to control ozone and carbon monoxide, two of the most stubborn pollutants. But most argue for new federal pollution controls tied to the deadline extension, such as the adoption of auto maintenance and inspection programs and industrial emission cutbacks.

"It is unwise policy that represents nothing more than the granting of more time and a withdrawal of active federal participation," said Sen. George J. Mitchell (D-Maine), chairman of the environmental protection subcommittee and sponsor of a bill linking a compliance schedule to controls.