The Environmental Protection Agency yesterday announced a one-year delay in tougher pollution standards for heavy trucks that would require a 90 percent reduction in hydrocarbon and carbon monoxide emissions below 1970 levels.

The standards, set by Congress in the 1977 amendments to the Clean Air Act, would require truck manufacturers to install catalytic converters in 1984 heavy-duty models and were bitterly opposed by industry spokesmen.

EPA officials said they are considering easing the standard -- as called for by President Reagan's regulatory reform plan for the auto industry -- but will not reach a decision in time to enforce it this year "because manufacturers need to make product decisions for the approaching 1984 model year," an EPA spokesman said.

While delaying the tailpipe emissions standard, EPA announced a crackdown on "evaporative emissions" -- hydrocarbons that escape in fumes from other parts of trucks -- and on emissions from light-duty trucks sold in high altitude areas.

Starting in 1985 models, the agency will regulate trucks weighing 8,500 pounds or more to bring about a 92 percent reduction in hydrocarbons escaping from parts of trucks other than the tailpipe, officials said.

EPA officials estimated these changes would add about $42 to the cost of the average truck. The new rule for light-duty trucks (those weighing up to 8,500 pounds) will take effect in 1984 models, requiring a 50 percent cut in hydrocarbon emissions compared to 1983, and almost the same cutback for carbon monoxide emissions. This will add $9 to the cost of small trucks, EPA said.

Taken together, EPA assistant administrator Kathleen Bennett called the three announcements a sign of "balance" in EPA's pollution control program.

However, the delay in the emissions controls for heavy trucks came under fire from environmentalists, who called them essential to reducing carbon monoxide and ozone in heavily polluted urban areas.

EPA proposed earlier this year to repeal the requirement for a 90-percent reduction in heavy truck emissions, but delayed any change after critics produced studies showing the standard would save consumers more than it would cost, because of improved gasoline mileage.

"They've got a proposal that doesn't make environmental or economic sense," said David Donagher of the Natural Resources Defense Council. "Basically, what they're trying to do is to buy a year because they can't figure out a way to live up to their promise to the auto industry to repeal this standard."