The Environmental Protection Agency yesterday proposed a grace period of up to eight years for most metropolitan areas to reduce the amount of ozone and carbon monoxide pollution in their air.

The plan would free more than 50 cities and their suburbs, including metropolitan Washington, from the immediate threat of EPA construction bans for failing to meet federal air-quality standards for the two pollutants by the law's deadline of Dec. 31.

States would be required instead to come up with a new plan within the next two years designed to achieve the standards by 1996. Although the most intractable cities would be forced to halt construction of new industrial facilities, they could stave off other sanctions, including the withdrawal of federal highway funds, as long as they cut carbon monoxide and ozone by 3 percent yearly.

EPA Administrator Lee M. Thomas called the plan, which is subject to a 60-day review period, "tough but reasonable."

But despite the extra leeway, state officials sharply criticized Thomas for shifting responsiblity to local jurisdictions for the politically sensitive measures, such as car pools, needed to achieve the air-quality standards in the most polluted areas.

"We're far more successful in reducing emissions when the federal government takes an aggressive role in prescribing reasonable control measures," said William Becker, executive director of State and Territorial Air Pollution Program Administrators. Becker and state officials called specificially for EPA to impose further cutbacks on auto emissions and gas pump controls to reduce toxic vapors -- measures now being considered by Congress.

"The whole point of sanctions has been to stimulate action to clean up pollution," said Richard Ayers, chairman of the National Clean Air Coalition. "If you delay them, you take off that pressure. The states then relax and we go back to drifting."

Carbon monoxide, emitted chiefly by automobiles, can cause circulatory problems. While ozone high in the atmosphere helps to shield the Earth from harmful ultraviolet rays, ozone at low altitudes -- formed by the mixture of hydrocarbons released from cars and factories -- can result in pulmonary and respiratory trouble.

The Clean Air Act of 1970 set standards for reducing the two pollutants. States were originally expected to meet the standards in 1975, but Congress extended the deadline until this Dec. 31 while directing governors to submit plans for cleaning the air of their metropolitan areas.

Last June, the EPA proposed construction bans for 14 areas that had failed to craft adequate plans. Another 53 areas are expected to fall short of the standards for either carbon monoxide or ozone by Dec. 31. The Washington area only slightly exceeds the ozone limit but fails to meet the carbon monoxide standard by 50 percent.

Thomas said at a news conference that a ban on construction of new plants will be imposed, as planned, in all but one of the 14 areas cited in June, including Los Angeles, Cleveland and Chicago.

But instead of imposing construction bans on the 53 other metropolitan areas, the EPA will require state governments to submit new plans by the spring of 1990 demonstrating how they plan to bring the areas into compliance within three to five years, depending on the severity of their pollution. States would be able to choose their own antipollution strategy, as long as it results in a 3 percent annual reduction of carbon monoxide and hydrocarbons.

The agency will take a year, ending in the spring of 1991, to review the plans. EPA officials said they expect that half of the 53 areas, including metropolitan Washington, will be able to demonstrate compliance within the required time.

At least 20 areas are so polluted that the three-to-five-year deadline is unrealistic, officials said. Those areas would be subject to construction bans, which would remain in effect until officials could show that they were able to reduce pollution within the prescribed time. As long as they reduce the pollutants by 3 percent per year, however, they would avoid more stringent penalties, such as cutoffs of federal highway, sewage-treatment and air-pollution grants, officials said.

According to this strategy, Los Angeles is expected to take at least 20 years to meet ozone and carbon monoxide standards.

Thomas called the 3 percent annual cutback an "aggressive percentage," which would require "very tough decisions," including expansion of mass transit or car pools in such polluted cities as Los Angeles, Denver and New York.

Asked why the federal government did not prescribe pollution controls to assure compliance, he said that elected officials at the state level "don't want to abdicate their responsibility." He said states, which have failed to attain the standards in the past 17 years, will now be motivated because "they have a realistic program rather than an arbitrary process" of automatic sanctions.