At least 10,000 people are working as forced laborers at any given time across the United States, according to a new report that details the nature and extent of "modern-day slavery." The study says the laborers are working for little or no pay on farms, in restaurants and sweatshops and as domestic servants and prostitutes.

The report, "Hidden Slaves: Forced Labor in the United States," is to be released today on Capitol Hill by the University of California at Berkeley's Human Rights Center and the Washington-based anti-slavery group Free the Slaves.

Most people think slavery is a problem that was solved long ago, said Laurel Fletcher, one of the study's authors and a professor at UC Berkeley's law school. "But in fact, it's alive and well. It has simply taken on a new form," she said.

Forced labor has been documented in at least 90 U.S. cities, including some Washington area communities, and it is concentrated in poorly regulated industries with a high demand for cheap labor, the study says. Most victims are trafficked into the United States through force, fraud or coercion and are brought from more than three dozen countries, with China, Mexico and Vietnam topping the list, researchers said.

Most cases are in heavily populated states that have large immigrant communities, such as California, Florida, New York and Texas. In the Washington area, cases were reported in the District, Alexandria, Falls Church and Silver Spring.

The report is based on a survey of 49 service providers involved in forced-labor cases, eight case studies and an analysis of 131 incidents reported in the U.S. media, most of which involved many victims, the report said.

The report's figure of 10,000 is less than a U.S. Justice Department estimate that at least 14,500 people are trafficked into the country annually. But cases often are hidden and victims are afraid to report the abuse to authorities, making it difficult to pinpoint a number.

"That's 10,000 major crimes," said Kevin Bales, a co-author and president of Free the Slaves, who ranked enslavement "right up there with torture and kidnapping and murder." Employers use physical and psychological violence to hold victims captive, confiscating passports and threatening to harm family members.

In one case, a Texas faith-based mission group recruited dozens of young boys from Zambia to perform in church choirs in Texas and other states. The boys performed several times daily, but never were paid or allowed to go to school and were forced to do hard physical labor, Bales said. He said the U.S. government needs to raise public awareness of the problem and train more local police to recognize signs of trafficking and forced labor.

In another case, a Mexican woman forced to work in a Los Angeles sweatshop said she was regularly beaten by her trafficker. She had been recruited to the United States with promises of a job and free room and board.

Instead, she was forced to work 17-hour days making silk party dresses and was given one daily meal of rice and beans. She was paid about $100 a week and was forced to pay off a "debt" of $2,550 to the trafficker, she said in a telephone interview.

Guards outside the sweatshop prevented her from leaving, and the trafficker -- who owned the sweatshop -- threatened to call authorities if she tried to escape. Eventually, local police raided the factory after receiving a tip. U.S. officials investigated her case and granted her permission to stay in the United States under a 2000 federal law to combat trafficking.

The woman, 32, fears for her children's safety in Mexico. The trafficker recently contacted the woman's family in her hometown of Pueblo, she said.

"Sometimes I feel like I want to fly or run to my kids," said the woman, who did not want her name used because she feared retaliation by her trafficker. "I pray for them every day."

Staff writer Darragh Johnson contributed to this report.