The Environmental Protection Agency announced plans yesterday to require air pollution controls for municipal waste incinerators and released a study showing long-term cancer risks of dioxin and other chemicals discharged by the facilities.

Environmentalists have urged stringent limitations on emissions from the incinerators, which are expected to play an increasingly important role in disposal of domestic wastes as the nation's landfill capacity dwindles.

Under a two-step program, the EPA will require new facilities to contain the latest pollution control devices as a condition of operating. The requirement can be waived if the owner of the incinerator can prove the devices are not necessary to minimize risk.

Regulations will be proposed in 1989 to limit emissions of new facilities to the lowest attainable levels, and the EPA will require states to upgrade the 111 incinerators operating today if they exceed the standards.

Installation of the control devices is expected to add $300 million a year to the costs of new facilities and up to $200 million a year for existing plants.

Assistant EPA Administrator J. Winston Porter said the health risks of trash burners are "fairly small" but do warrant controls by the best technology available.

Without controls, dioxin emissions could cause three to 38 additional cancer cases annually nationwide for people exposed over a lifetime, according to the EPA. Fewer than one extra case would result from exposure to other carcinogenic substances released by the facilities, including chlorobenzenes and polychlorinated biphenyls (PCBs).

Control devices that trap or clean the chemicals can reduce emissions by up to 99 percent, Porter said.

The EPA's decision ran into opposition yesterday by the National Resources Defense Council and some members of Congress. They argue that the best technology may not be good enough to reduce emissions to safe levels.