ASHINGTON, Sept. 10 — The National Academy of Sciences has concluded that arsenic is so dangerous in drinking water that stringent levels set by the Clinton administration and later suspended by the Bush White House were justified but perhaps not strict enough.
Details of a report by the academy that were made available tonight by government officials, give the Bush administration little latitude in which to maneuver on this sensitive issue, one that even President Bush has acknowledged was a public relations disaster for his administration.
For decades, the Environmental Protection Agency set an acceptable arsenic level of 50 parts per billion in drinking water. But recent studies suggested that this level was too high and increased the risk of bladder and lung cancer. A report by the National Academy of Sciences in 1999 said the standard should be made stricter "as promptly as possible." President Bill Clinton ordered the limit to be lowered to 10 parts per billion in 2006.
The Bush administration suspended the Clinton ruling on March 20, drawing a wave of protest that it was more sympathetic to the chemical industry than to consumers. Officials said they were re-evaluating the levels and would wait for the new report by the academy before determining whether to set the level at 3 parts per billion, or 5, 10 or 20.
A senior administration official said tonight that the report found an increased risk of cancer if the level was above 10 parts per billion.
"We are not considering anything higher than 20," this official asserted. And another said: "We may be looking at something lower than 10, but we have an awful lot to look at. It's not inconceivable."
The officials said that Christie Whitman, the administrator of the E.P.A., would make a ruling by February of next year.
By signaling that a prudent level might be lower than 10, the report, which was based on a review of 300 recent arsenic studies, will put enormous pressure on the administration to stay at that level or below.
"It boxes them in," said Joan Mulhern, legislative counsel for the Earthjustice Legal Defense Fund. "With the public and the Hill, there is tremendous political pressure already to adopt the standard of 10 or something more strict. If this is what the National Academy is saying, it pretty much closes the door on the administration doing anything higher than 10."
The House passed a bill earlier this year saying the limit should be no higher than 10. The Senate did not specify a number but said that the administration needed to set a standard immediately that protected sensitive populations like children and the elderly.
The 10 parts per billion standard for drinking water set by the Clinton administration was the same as the one set by the World Health Organization and most European countries.
At least 13 million Americans, most of them in small towns and rural areas but some in cities as large as Albuquerque, rely on drinking water that contains more arsenic than the 10 parts per billion that would have been allowed under the Clinton rules, officials of the Environmental Protection Agency said.
The arsenic decision by Ms. Whitman in March was among the most explosive of the administration's early days and one that even President Bush has acknowledged was part of a chain of events that made the administration appear tone-deaf on environmental issues.
"I think we could have handled the environmental issue a little better," Mr. Bush said in an interview last month with ABC News, pointing in particular to the arsenic decision. But he defended Ms. Whitman's suspension of the Clinton standard, saying she had "pulled back a rushed piece of legislation to look at it, to make sure the science was sound, and therefore we got labeled for being for arsenic in water."
Ms. Whitman has said she regretted the decision.
"Politically, if I'd been smart, I would have never changed it," Ms. Whitman told USA Today last month. "I never would have gone back. I would have let the courts decide. We were going to be sued anyway by the Western states and a bunch of water companies, and I should have just left it there."
The Clinton decision to lower the level to 10 parts per billion was challenged by several Western states, utilities and the mining industry. Municipalities that would have to correct their water systems have argued that the cost to them would far outweigh the benefits to the public in cleansing arsenic, which occurs naturally, out of drinking water.
Arsenic is a common byproduct of mining operations, so stricter standards for its content in drinking water would translate into stricter standards for many mining sites.
The wood products industry had supported the Bush administration's ruling suspending the Clinton ruling because arsenic is used to pressure- treat lumber.
The report by the academy examined only the public health consequences of arsenic and did not conduct a cost-benefit analysis for water suppliers.
Environmental groups have wrung considerable political mileage from the arsenic decision and hope to add to the administration's discomfort by broadcasting new television commercials in eight states and the District of Columbia starting on Tuesday. The commercials show a rat eating arsenic and note that arsenic causes cancer in people. The commercials, at a cost of $100,000, are intended to pressure the administration to set safer arsenic levels — and also to suggest to voters in markets with major elections this fall that the Republican administration would sacrifice public health for the profit of special interests.
The commercials were timed to coincide with the public comment period on the arsenic rule, which is to begin next week.
A team from the academy briefed Ms. Whitman for 45 minutes tonight on the report and is to brief members of Congress on Tuesday.
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