WASHINGTON, Oct. 31 — The Environmental Protection Agency today proposed a new standard that would double the maximum permissible level of fluoride in the nation’s drinking water supplies.

The new maximum, four milligrams to a liter of water, is well above levels that can cause dental fluorosis, which results in discoloration, mottling and pitting of teeth according to the environmental agency. The agency said, however, that a report issued by the Surgeon General of the United States in 1982 held that fluorosis was not an adverse health effect.

Fluoride is often added to drinking water supplies as a means of combatting tooth decay. About half of all water systems in the country are fluoridized.

Fluoride also occurs naturally in some water supplies. Under the old maximum levels, a number of communities, including many in South Carolina, were forced to spend considerable amounts of money to reduce fluoride levels. South Carolina has sued the environmental agency to change the standard.

Environmentalists protested the proposed new levels, saying they could cause serious health problems.

Jacqueline M. Warren, senior attorney for the Natural Resources Defense Council, an environmental group, called the proposal ”outrageous.” She said that the environmental agency has evidence that the higher levels of fluoride has caused skeletal fluorisis, a condition that makes bones hard and brittle.

Her organization intends to sue to block the new standard she said.

Scientist Disputes Decision

Robert Carton, a scientist with the environmental agency’s health and environment office, said that the professional staff of the agency had recommended keeping a lower maximum level for fluoride and that the decision by the agency raises ”terrific questions about the quality of the support science that went into the decision.”

He also said that many psychologists have said that the disfiguring of teeth by fluoride constitutes a potential health problem.

Mr. Carton was recently elected president of the National Federation of Federal Employees local representing professional employees at the agency. He said he was sending a letter protesting the decision on the ground that it raised concerns about the professional reputation of scientists in the agency.

A spokesman for the agency, Michael Reilly, said that there were only two cases known in the United States where consumption of water that containing fluoride at four milligrams per liter had caused fluorosis. He said he did not not know that the decision had reversed a recommendation of the professional staff.

”But it is a very controversial issue,” he said.

The environmental agency has set hearings on the proposed new rule for Dec. 18 and will accept comments on the proposal until the end of the year.

Agency Suggests Best Levels

The agency statement today said that at levels of one to two milligrams to a liter fluoride did protect teeth. In addition to proposing the new maximum level, the agency also proposed a ”secondary maximum contaminant level” of two milligrams to a liter, which it said ”is intended to provide guidance to states and communities for limiting the occurrence of dental fluorosis while still permitting optimal fluoride levels for the reduction of cavities.”

The agency said that the secondary standard was not ”federally enforcable.”

The agency also stated that at four milligrams to a liter and above, fluoride ”can cause changes in bone density which cause no detectable health effects.” It added, ”At 10 milligrams per liter, long-term exposures can cause sekletal disorders similar to arthritis.”

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