WASHINGTON - President Bush yesterday signed legislation to protect people from losing their jobs or health insurance when genetic testing reveals they are susceptible to costly diseases.

Broadly embraced in Congress, the measure aims to ensure that advances in DNA testing won't end up being used against people.

The new law forbids employers and insurance companies from denying employment, promotions or health coverage to people when genetic tests show they have a predisposition to cancer, heart disease or other ailments.

Bush praised the bill for protecting "our citizens from having genetic information misused."

Sponsors of the legislation call it a groundbreaking protection of civil rights. About a dozen of them gathered in the Oval Office as Bush signed the bill, but not Sen. Edward M. Kennedy, to whom the president paid particular tribute.

Kennedy, who learned this week that he has a malignant brain tumor, has called the bill "the first major new civil rights bill of the new century." The Democratic senator from Massachusetts left the hospital yesterday.

People today have far more information about their hereditary disposition to crippling afflictions. Bill sponsors said that had increased the likelihood that insurers or employers might deny people work or insurance to avoid costly risks.

"This is a tremendous victory for every American not born with perfect genes - which means it's a victory for every single one us," said Rep. Louise M. Slaughter (D., N.Y.), one of the bill's key sponsors.

Genetic tests look for alterations in a person's genes, and abnormal results can mean that someone has an inherited disorder. The tests look for signs of a disease or disorder in DNA taken from a person's blood, body fluids or tissues.

Researchers have supported the bill because Americans have been refusing to take genetic tests or have been using false names and paying cash because they did not want the information used against them by their employer or insurance company.

The new law prohibits health-insurance companies from using genetic data to set premiums or determine enrollment eligibility.

A 2001 study by the American Management Association showed that nearly two-thirds of major U.S. firms require medical exams of new hires.