The arrest of black Harvard professor Henry Louis Gates Jr., for “disorderly conduct” has set off a debate about racial profiling across America. But for civil libertarians, the incident on a front porch in Cambridge, Mass., raises a different issue: what they see as a subtle growth in police power since the war on drugs and 9/11, exemplified in so-called “attitude arrests” – when someone challenges or fails to show deference to police authority.

In Mr. Gates's case, police described his behavior as "tumultuous," but he broke no discernible laws. The Cambridge Police Department conceded as much when it dropped the charges, calling the incident "regrettable." The local police union backs the arresting officer, who said he did nothing wrong.

"What I see as more significant [than race] is the phenomenon of persons being arrested who challenge the authority of police," says David Rudovsky, a senior fellow at the University of Pennsylvania Law School in Philadelphia. "It's street punishment."

Nearly all police jurisdictions have so-called "cover charges" such as "disturbing the peace" or "disorderly conduct," which are intended to protect police officers from threat of violence. The extent to which prosecutors and booking officers accept arrests under such charges – which are often defined vaguely – varies widely across the country. Some civil liberties advocates say that these arrests can be subjective, and sometimes a response to back talk.

"To put cuffs on somebody is a grave matter, and it has to be for more than an officer just having a bad day," says George Kirkham, a former cop who's now a criminology professor at Florida State University in Tallahassee. As employers and others increasingly use background checks, even a trivial arrest can be potentially damaging.

And subjective arrests of people who challenge an officer's authority also undermine community trust needed to catch and investigate real criminals, says Radley Balko, a senior editor at Reason Magazine.

Police defenders counter that the citizenry needs to respect officers who, day in and day out, perform a dangerous job, with few accolades.

"The rule is, if a police officer stops you in a car or on the street, he's the captain of the ship, and whatever he says goes," says Jim Pasco, executive director of the Fraternal Order of Police's legislative division. "If you've got something to address, do it later. Do what he says, or else only bad things can happen."

Some critics suggest the task of training officers has become more difficult since the war on drugs, the "militarization" of US police through the growing use of SWAT teams for even minor antidrug operations, and the increasing use of Taser guns.

They worry that officers lose what former Seattle police chief Norm Stamper calls "the emotional resilience to understand situations like this, and defuse them."

"The fact is we have the First and Fourth Amendments that protects very basic rights of American citizens, and I think it's critical that police officers understand that their work has to not only be skillful and competent, but constitutional," says Mr. Stamper.

[Editor's note: The original version left out the opening paragraph.]