Illegal immigrants cost the federal government $10 billion more in services than they contribute in taxes, according to a report released Wednesday by the Center for Immigration Studies, a conservative research organization in Washington, D.C.

Gleaning information from the U.S. Census and other sources, authors of the report, called the High Cost of Cheap Labor: Illegal Immigration and the Federal Budget, offers a complex fiscal picture of the illegal immigrant population.

The report drew criticism from some pro-immigrant groups, saying that the researchers did not paint a full picture of the contributions illegal immigrants make through their labor and purchasing power.

Despite popular notions that illegal immigrants abuse welfare services and don't pay taxes, the report concluded that this segment of the population receives relatively few resources and contributes $16 billion in federal taxes.

Nevertheless, the report's principal author, Steven Camarota, said that if presidential candidates fulfill their pledges to offer amnesty to the country's estimated 8.7 million illegal immigrants, the cost to provide services for them could triple to $29 billion.

"Ten billion isn't chicken feed," Camarota said. "It's not trivial."

Much of the cost of illegal immigration is attributed to relatively low educational levels among immigrants, Camarota said. Little education translates to low-paying jobs with few benefits. Fewer employment benefits lead to a greater need for government services, he said.

The federal government pays about $2.2 billion in medical treatment for uninsured immigrants, according to the report. It pays $1.9 billion in food assistance programs, such as food stamps and school lunches, for low-income families. And it pays $1.4 billion in aid to schools that educate illegal immigrant children.

Moreover, there are unavoidable costs, according to the report. Those costs include federal courts and prisons that punish illegal immigrants charged with crimes and costs associated with aid to U.S.-born children of illegal immigrants.

The report does not include the costs of state and local governments, which share in the burden of paying for illegal immigration.

The report also does not address the broader contributions made by illegal immigrants, such as profits their employers generate or the sales taxes immigrants pay for goods they purchase, critics of the report said.

"It's a polemical debate that has no end," said Arturo Navarro, a professor of ethnic studies at UC Riverside and a Latino activist. "Our people are not driven to risk their lives crossing the border by the dream of becoming welfare recipients. They are driven by the American Dream."

Even some who support more strict immigration controls said they were suspicious about the report's findings. Freeman Sawyer, a local anti-illegal immigrant activist, said he questioned how the researchers arrived at their figures.

"If I go to Temecula (Valley) High School, even with a court order in my hand, and I said, 'I want to know how many illegal aliens are here; how many are receiving free lunches?'… They are not going to give them to me," Sawyer said.

He added: "I don't understand how they were able to get (data) from a population that doesn't want to be found."

Other findings of the report include:

• On average, the costs that illegal households impose on federal coffers are less than half of other households, but their payments are less than a third of other households.

• The vast majority of illegal immigrants hold jobs. Thus, the fiscal deficit they create for the federal government is not the result of an unwillingness to work, according to the report.

• Although legalization would increase average tax payments by 77 percent, average costs would rise by 118 percent.

Read the full report at: http://www.cis.org/articles/2004/fiscalrelease.html.

Contact staff writer Edward Sifuentes at (760) 740-5426 or esifuentes@nctimes.com.