About 50 county police officers participated in the joint operation with Immigration and Customs Enforcement. Units fanned out at 6 a.m., with officers targeting Annapolis Painting Services, where many of the workers were employed. The raid also included 15 residences, County Executive John R. Leopold said.

"This will send a very strong signal that this administration, with the cooperation of ICE, will not tolerate the hiring of illegal immigrants in this county," he said, standing across the street from the painting company's building.

The two-story red building on Housley Road near Westfield Annapolis mall was buzzing this morning, as employees waited and investigators towed vehicles and removed boxes of evidence from the premises.

Col. James Teare Sr. said officers were pulled from other details in all areas of the department to help with this morning's operation and that regular police patrols were not affected.

"This is a coordinated effort that was well planned out," the county police chief said.

The 45 immigrants were taken by ICE officials to a processing center. ICE officials will determine where they will go and will work with social services and other organizations to notify family members, Chief Teare said.

Annapolis Painting Services officials could not be reached for comment by press time.

The operation is part of an ongoing effort to remove immigrants who are illegally in the country from Anne Arundel County. Predominantly, large numbers of the workers are found in manual labor jobs, though they can be found in other jobs as well, Chief Teare said.

Mr. Leopold stressed this has been a priority throughout his administration.

"Illegal means illegal. There must be a respect for the law," he said, noting that businesses that employ illegal workers put other businesses at a disadvantage because illegal workers are often paid less.

He said there have been four operations of this kind since he took office.

Last fall, Mr. Leopold permanently assigned a county police officer to the regional Document and Benefit Fraud Task Force, which is led by ICE.

Also, one officer from each of the county police department's four districts has received specialized training in spotting fake immigration documents and assisting in immigration investigations.

The county also is more quickly notifying ICE officials when immigrants are arrested or held in county jails, so that ICE can check whether they are here legally. The policy of making on-the-spot notifications rather than weekly notifications went into effect in April.

That policy has drawn fire from immigrant-assistance groups, who said it would breed fear and distrust.

And last spring, Mr. Leopold cut funding to nonprofit groups that did not discern between aiding legal and illegal immigrants.

In August, he issued an executive order requiring all contractors hired by the county to sign an affidavit swearing the company does not hire illegal workers.

At the same time, however, Mr. Leopold pushed for a workshop earlier this year to help businesses navigate the complicated process of legally hiring foreign workers.

Immigration continues to rise in Anne Arundel County and across the nation. Census figures show Anne Arundel's foreign-born population grew 32 percent from 23,211 in 2000 to 30,748 in 2006.

Local economic development officials have said there are perhaps about 175,000 workers in Maryland illegally, representing about 6 percent of the workforce.

Staff writer Pam Wood contributed to this report.