WASHINGTON (AP) _ The Environmental Protection Agency on Friday banned the use of mercury in interior paints because of possible poisoning from inhalation and other exposure.

''EPA and the registrants of mercury paint preservatives have agreed to ban the use of mercury in indoor paint effective Aug. 20, 1990,'' said Linda Fisher, assistant administrator for pesticides and toxic substances.

Manufacturers must eliminate mercury from all new interior paint formulas, said Fisher.

Mercury is regulated as a pesticide by the EPA.

Mercury compounds are used as a preservative in about 30 percent of the water-based latex paint products currently on the market. Oil-based paints do not contain mercury.

Despite uncertainty about how long inhalation risks exist, the agency did not recommend paint removal or repainting areas covered some time ago but said ''painted rooms should be thoroughly and frequently ventilated.''

Although the ban does not extend to exterior paint, the agency will require new warning labels to inform consumers when paint contains mercury.

Currently, paint labels are not required to indicate whether products contain mercury or not.

Existing dual-purpose or interior-exterior paints also will carry labels. However, no new dual-purpose products can contain mercury.

In addition, mercury preservative manufacturers must submit new testing data to determine the potential risks for continued outdoor use of mercury- containing paints and other products.

Store merchants must add the labels to paint currently on their shelves which contain mercury at levels higher than 200 parts per million.

The new labels also must stress that those products should be limited to outdoor use, warn of potential health hazards and caution against exposure to children.

''The EPA believes tat consumers may continue to use interior paint with lower mercury levels without unreasonable risk if they follow all label directions, ventilate thoroughly, both during and after use, and minimize exposure to children,'' Fisher said.

The EPA will provide information to the public on specific paints on the National Pesticide Telecommunication Network at 1-800-858-7378.

The agency estimated it would take three months to get the new products on the market.

It warned consumers who wish to dispose of mercury-containing products not to pour them down a drain, into a ditch or into any body of water but to contact government officials or community hazardous waste programs.

Other products - acoustical plaster, adhesives and spackling and joint compounds - generally used in construction work, also contain mercury.

''Only a ban on use of existing stocks and product recall will prevent unacceptable public exposure,'' said Catherine Karr, a toxicologist for the National Coalition Against the Misuse of Pesticides, in a written statement.

The agency's actions were prompted by a case of severe mercury poisoning, or acrodynia, in a 4-year-old Michigan boy when his home was being painted last year. After four months of intensive blood-cleansing therapy the child has almost fully recovered, said Dr. William Roper, director of the federal Centers for Disease Control.