You're a bank robber in Cambridge.

You've just emptied a safe and are about to make a frantic dash for your secret hideaway in the city's alleys.

Your plan thus far has been perfectly executed--a ski mask covered your face, gloves hid your fingerprints and transportation by foot averted possible license plate identification.

Your only remaining task is evasion of the police. Which shouldn't be a problem, you think, because police cars can't successfully chase you through the narrowness of the back alleys.

But beginning yesterday, your grand plan for an easy escape over rough or narrow terrain would be more easily foiled by the local cops.

In an attempt to provide added mobility to its squads, the Cambridge Police Department unveiled a new bicycle unit yesterday.

Six police officers will protect and serve Cambridge on 10-speeds. The cops will respond to emergency calls and patrol the city, "just like normal cops, only on bikes," says Frank T. Pasquarello, a police spokesperson.

The key advantage to cops on bikes, Pasquarello says, is increased access to sites not reachable via automobile, at a higher speed than is possible on foot.

Bikes should also be easier to maneuver through Cambridge's maze of one-way, narrow streets.

The Square, for example, is usually congested during the daytime. Police driving a car might have difficulty plowing down Mass. Ave. to catch a suspected criminal. But a cop on a bicycle could advance through the cars more easily, Pasquarello said.

And the bike unit's inaugural day on the jobprovided evidence for its utility.

According to Pasquarello, a plain clothesdetective in Columbia Park Terrace spotted a mansuspected of outstanding warrants yesterday ataround noon.

The suspect started running and was uncatchableto a cop in a car. But the police on bikes wereable to chase the suspect and arrest him on theother side of the park.

Still, Pasquarello says such incidents areprobably fairly infrequent.

"It's difficult to really pinpoint" how manyalleged criminals escape from the police becausethey're uncatchable by car, Pasquarello says."It's not that many."

But the bicycle-riding police serve anotherfunction besides apprehending criminals--impro@[relations between cops and civilians.