Federal agents have arrested 33 illegal immigrants at the Pentagon, about one in six of the employees who were asked to produce work permits during a surprise raid on construction crews hired for the building's $1.2 billion renovation, officials said yesterday."

Authorities refused to identify companies that employed the immigrants arrested in the Thursday raid. Agents are still investigating whether the firms knew they had hired undocumented workers, officials said, adding that they will continue to monitor the Pentagon's construction work force to determine whether others are employed illegally.

Pentagon spokesman Glenn Flood said as many as 500 construction workers are employed at various sites inside and outside the building on any given day. Investigators with the U.S. Immigration and Naturalization Service and the Defense Protective Service, the Pentagon's police force, examined the documents of about 200 of them as they showed up for work, he said.

INS spokesman Josh Green said 29 of the 33 undocumented workers, who are from Costa Rica, El Salvador, Guatemala, Honduras, Mexico and Nicaragua, have been detained at the Pamunkey Regional Jail in Hanover, Va. They face deportation hearings and possible prosecution for possession and use of fraudulent documents, he said.

Three other workers were released because they have pending immigration cases, Green said, and a fourth worker, a juvenile, was released to his family.

Flood said all workers on the project receive special passes from the Pentagon allowing them into construction areas, but none had access to other parts of the building. He said contractors submit Social Security numbers and other information about workers to the Pentagon to obtain the passes.

The Pentagon did not conduct background checks on the workers. But Flood said officers last month noticed that several of them were using the same Social Security numbers and contacted the INS.

The renovation project, which includes the construction of a new building in one of the Pentagon's parking lots, has been underway for several years, but this is the first time the Pentagon and INS have scrutinized it for illegal workers.

Several community activists expressed concerns about the raid, saying workers reported that the agents flushed them out of the building with a false alarm about a bomb threat, then asked only Latino employees for proof of work authorization.

"Obviously, there's not such a thing as a friendly raid, but they violated every procedure in the book," said Jessica Alvarez, of the Council of Latino Agencies.

"We're concerned about whether they singled out all Latino workers in asking for work permits," said Abel Nunez, president of the Organization of Salvadoran Americans.

"That sounds like a civil rights violation. We're seeking more information."

Flood denied that agents used the ruse of a bomb threat during the operation, saying workers were questioned as they punched in at a time clock.

INS spokeswoman Amy Otten said the agency did not violate any of its procedures during the raid.