DENVER — The federal government is rapidly expanding a program to identify illegal immigrants using fingerprints from arrests, drawing opposition from local authorities and advocates who argue the initiative amounts to an excessive dragnet.

The program has gotten less attention than Arizona’s new immigration law, but it may end up having a bigger impact because of its potential to round up and deport so many immigrants nationwide.

The San Francisco sheriff wanted nothing to do with the program, and the City Council in Washington, D.C., blocked use of the fingerprint plan in the nation’s capital. Colorado is the latest to debate the program, called Secure Communities, and immigrant groups have begun to speak up, telling the governor in a letter last week that the initiative will make crime victims reluctant to cooperate with police “due to fear of being drawn into the immigration regime.”

Under the program, the fingerprints of everyone who is booked into jail for any crime are run against FBI criminal history records and Department of Homeland Security immigration records to determine who is in the country illegally and whether they’ve been arrested previously. Most jurisdictions are not included in the program, but Immigration and Customs Enforcement has been expanding the initiative.