To hear civic leaders tell it, the expense of cleaning up polluted storm water in Los Angeles County will greatly exceed the cost of waging war on Iraq. The price tag will be bigger than the gross national product of all but 16 of the world's largest countries. At $283.9 billion, it would be the equivalent of assessing every man, woman and child in America about $1,000.

The mostly inland cities that make these claims are battling in court to block enforcement of storm water provisions of the Clean Water Act that require them to prevent a toxic stew of oil, pesticides, dog droppings and human sewage from washing into the ocean and onto beaches every time it rains.

On Tuesday, they released a study by USC economists and engineers that claims the region would need to build between 65 and 130 water treatment plants, resulting in economic losses of up to $170 billion and up to 214,000 jobs.

"It's a staggering waste of our taxpayer dollars," Downey Councilman Keith McCarthy said at a news conference at USC to release the $102,000 study commissioned by about 20 cities. "It will be the people in our towns who will suffer lost jobs, cutbacks on public safety and other [municipal] programs."

State and federal officials who attended the news conference characterized the study figures as "absurdly inflated" and "propaganda."

"It's ludicrous," said Fran Diamond, chairwoman of the Los Angeles Regional Water Quality Control Board, a state agency. The real cost of meeting clean-water rules, she said, is about $50 million a year based on cities' own reported expenditures.

"They sound like Chicken Little," said Catherine Kuhlman, acting regional director of the federal Environmental Protection Agency's water division. "But the sky is not falling."

Those two agencies, which enforce clean-water rules to clean up pollution in Santa Monica Bay and Los Angeles Harbor, said the USC study was fundamentally flawed because it was based on a faulty premise.

They say the study errs by focusing on the cost of building enough treatment plants throughout the Los Angeles Basin to collect the billions of gallons of runoff that currently wash into storm drains and make it clean enough to drink by running every drop through a reverse-osmosis system.

Yet the rules do not require runoff to be made clean enough to drink, and regulators do not believe treatment plants of any kind will be needed.

So, they argue, the study should have measured the costs of other, less expensive approaches to satisfying the Clean Water Act provisions, such as improved street sweeping, cracking down on industries that spill pollutants into storm drains and educating the public on the misuse of pesticides.

The study, running various scenarios, concluded that between 65 and 480 treatment plants would have to be built to comply with all the new rules being imposed on cities to clean up the trash, bacteria and heavy metals swept to the sea during rainstorms.

As it stands, the region has no plants designed to treat storm water. It does have nine wastewater plants that handle billions of gallons of raw sewage — but those plants do not use the expensive reverse-osmosis systems that are necessary to convert storm water into drinking water.

H. David Nahai, past chairman of the regional water quality control board, said there is nothing in the clean-water rules that requires a single treatment plant to be built, much less 65 of them.

"What we have here is propaganda," Nahai said, raising an objection during the news conference. "The authors of this study are either unwitting pawns or willing accomplices."

At least one of the principal authors of the report, public policy and economics professor Peter Gordon, seemed to relish how the study had gotten under the skin of regulators.

"After all these years," Gordon said, "I'm pleased to understand that regulation is inexpensive and benign."

James E. Moore, a USC professor of engineering, defended the study and its basic premise that the cities would have to build at least 65 treatment plants to strip runoff of bacteria, heavy metals and other pollutants.

"The need for advanced [water] treatment is a credible outcome," Moore said, although he acknowledged there may be cheaper ways.

The study calculates it would cost $283.9 billion to buy land and build the treatment plants. By financing such an enormous building project with bonds, the study concludes that the tax burden on the region would cost 27,000 to 214,000 full-time jobs per year and result in a net economic loss of $23 billion to $170 billion.

As a point of comparison, President Bush's economic advisor recently estimated that a war against Iraq would cost the nation $100 billion to $200 billion.

The storm-runoff study was commissioned by the Coalition for Practical Regulation, which represents more than a third of the 84 cities in Los Angeles County now required to meet clean-water rules.

All but one of the cities that paid for the study are inland with economies that do not depend on coastal tourism.

Craig Perkins, Santa Monica's director of environmental and public works, said his seaside city has not found it difficult to comply with the Clean Water Act provisions, which were designed to protect public health and marine life. He was surprised at the high costs estimated in the USC study.

"They must have hired the ex-Enron accountants to come up with that figure," Perkins said.

Neither Los Angeles County nor the city of Los Angeles is a member of the coalition that paid for the study. But both have joined the smaller cities in suing over ever-tightening rules.

"All of the money that could be spent on addressing the problem of storm-water pollution is being spent on lawyers," said Los Angeles Councilman Jack Weiss, who voted last week against suing to nullify the rules.

In an unrelated development, the U.S. 9th Circuit Court of Appeals on Tuesday ruled that the EPA must do a better job tailoring storm-water cleanup rules for smaller cities outside the Los Angeles urban basin, such as Santa Barbara and Morro Bay, and make sure the public has a bigger say in what steps are taken.

Times researcher Maloy Moore contributed to this report.