It should have been an everyday arrest: The suspects were just being detained for riding between subway cars, police said. But the encounter turned into a harrowing shootout on a subway platform, leaving a suspect dead and an officer hospitalized with three gunshot wounds.

Officer Annmarie Marchiondo was in stable condition early today with a broken ankle, broken foot and a flesh wound near her hip, authorities said. Police said the slain suspect – a parolee who had served time for manslaughter – grabbed her around the neck during the confrontation yesterday evening and sprayed the Bronx subway station with five shots before other officers fired back and stopped him.

“Luckily, (Marchiondo’s injury) wasn’t worse,” Mayor Bloomberg told reporters after visiting the injured officer at the hospital last night.

Officer Marchiondo and two other plainclothes officers spotted Juan Calves, 51, and another man riding between subway cars on a southbound 4 train going from the Bronx to Manhattan, Police Commissioner Raymond Kelly said. Moving between cars is a violation of subway rules.

After the officers took the suspects off the train at the 176th Street station, Calves grabbed Officer Marchiondo in a head lock, pulled out a stolen, 9-millimeter gun and fired five shots on the platform, police said.

While Officer Marchiondo struggled to get free, the two other officers fired back with a combined 13 shots, killing Calves, police said.

Police said it wasn’t clear early today who had shot Officer Marchiondo, a 17-year NYPD veteran. She was hit in the foot, ankle and left side, just under her bullet resistant vest, police said.

Police officers raced to aid Officer Marchiondo, carrying her down a flight of stairs from the elevated subway platform, a witness, Jason Ramos, told reporters.

“They were determined to help this lady,” he said.

Police said the platform was not crowded at the time of the shooting, about 5:20 p.m. Still, witnesses described a chaotic scene as subway riders dashed out of the station and passers-by on the street below scrambled for cover.

Calves was freed on parole from prison two years ago after serving time for manslaughter, robbery, and attempting to promote prison contraband. The manslaughter conviction involved the killing of a fellow prison inmate at Attica Correctional Facility in upstate New York, police said.

The second man detained, whose name wasn’t immediately released, was being questioned.

The officers had been patrolling the subways to enforce the regulation that bars passengers from jumping subway cars.

“Officer Marchiondo and police officers like her are the reason why New York City subways are the safest in memory,” Mr. Kelly said Friday.