As officers step up ticket-writing for traffic violations, the New York Police Department is considering introducing a new weapon in its war on speeders, illegal turners, and driving cell phone users.

Drivers glancing into their rearview mirrors will not be able to distinguish the NYPD’s new cars from the rest of traffic – until they break a law. Then the lights in the windshield start up with the same intensity as the familiar V-formation of red and blue flashers fastened to the roofs of regular patrol cars.

Police officers call the new cruisers “slick tops” because their roofs are smooth, like typical passenger vehicles. The cars are clearly marked with police decals, but lack the clunky and easily recognizable shape of ordinary patrol cars.

“These offer us the ability to be low-key,” an NYPD spokesman, Joseph Gallagher, said. “It’s a variation on the traditional police car that has a number of advantages during patrols for officers.”

Police Compstat reports show that summonses issued for moving violations already are up by 9.7% this year compared with the same four-month period last year.

After a pilot program that lasted several months, the NYPD is considering whether to make two dozen slicktop Chevrolet Impalas a permanent part of the fleet of precinct cruisers that patrol neighborhoods.

The NYPD’s Highway Patrol has used slick tops for the last five years. Around the country, from major departments to small-town forces, such cars are frequently used to combat reckless driving on the highways.

The New York State Police added many slick tops to its fleet after Governor Pataki banned the department from using unmarked vehicles, which have no police decals, for routine moving violations.

“Many people, especially aggressive drivers, have their eye on the rearview mirror for that light bar on police cars,” a spokesman for the New York State Police, Glenn Miner, said. “Some say it’s sneaky, but it’s just easier to catch those who might be looking out for you.”

The addition of slick-top multipurpose cars would add a new species to the police patrols on the street. There are already unmarked police cars for undercover and detective work and marked cars with the siren rack for ordinary duty, as well scooters, horses, helicopters, and boats.

NYPD officials want to capitalize on the element of surprise in other categories of police patrol as well as traffic violations.

Smaller than the Crown Victorias most police officers drive, the Impalas can respond quicker to developing crimes throughout the city. One of the possibilities studied during the test phase was adding some of the cars to the city’s task forces, which are mobile units able to respond quickly to crime situations at any spot within the borough, Mr. Gallagher said.

Depending on the results of the final evaluation, the cars could either hit the streets as slick tops or be refitted as ordinary patrol cars with the rack of lights, Mr. Gallagher said.