WASHINGTON – President Bush has signed an executive order requiring contractors and others who do business with the federal government to make sure their employees can legally work in the U.S.

Mr. Bush signed the order Friday, and the White House announced it Monday.

The federal government has had some embarrassing moments when illegal workers have been discovered to be working for contractors it has hired, Homeland Security Secretary Michael Chertoff said in a news conference. For that reason, the government is trying to get its own house in order, he said.

"The federal government should lead by example and not merely by exhortation," Mr. Chertoff said.

The order says federal departments and agencies must require contractors to use an electronic system to verify that the workers are eligible to work in the U.S. Homeland Security operates the Web-based E-Verify system, which Mr. Chertoff said 1,000 employers a week are signing up to use.

E-Verify checks various government databases to make sure that an employee's Social Security number is legitimate and that it goes with his or her name. If there are problems, the person is tagged as a potentially illegal worker and must resolve the discrepancy.

Concerns about the system's effect on privacy were to be the topic of a House subcommittee hearing today.