A woman dropped her gym bag on the tracks of a crowded Upper East Side subway station yesterday — then made the fatal decision to jump after it as screaming straphangers watched in horror.

The 48-year-old victim, identified as Rose Mankos, was crushed by a northbound No. 6 train barreling into the 77th Street Station below Lexington Avenue as she tried desperately to claw her way back to the platform.

“She had one choice to make and seconds to make it,” said Alfonso McGruder, 55, of The Bronx, who witnessed the tragedy. “She didn’t make the one that would have saved her life.

“She tried to go under the platform because the train was bearing down on her. Then she tried to climb onto the platform, but she couldn’t do that. Then she just froze.”

Mankos lost her life trying to retrieve a nylon LeSportsac bag filled with exercise clothes, toiletries and her cellphone, sources said.

“People were yelling at the lady on the tracks when they saw the train coming,” said Hakeem Nhl, 53, a vendor on the opposite platform. “People were screaming, ‘Oh, my, God! Oh, my God!’ ”

Witnesses reported that the train operator sounded his horn eight times and attempted to brake.

“I think she just went into shock knowing that the train was seconds from hitting her. It looked like she just gave up,” McGruder said.

Mankos died as soon as she was struck at around 3:45 p.m.

“You could see some woman with her head stuck in between the train [and the platform] and her arms sticking out,” recalled witness Andrew Pistella, 30. “Some guy was screaming, ‘Is this real? Is this real?’ It looked like a mannequin.”

It was bedlam on the platform, with children, teenagers and old ladies shrieking hysterically, witnesses said.

“Who drops their [bag] down there, then jumps down there to get it?” Pistella asked.

Onlookers shouted for Mankos to lie down between the tracks or under the platform — perhaps thinking of “Subway Superman” Wesley Autrey, who saved a fallen passenger by climbing atop him in the trough between the tracks as a train rolled over them in 2007.

“I felt the thud when the train hit the body,” said Glenda Farr, 52, who was on the train. “I didn’t know it was a body. I lived upstate. You ever hit a deer or something? It was like that.”

A neighbor said Mankos lived alone in her Stuyvesant Town apartment.

NYC Transit spokesman Paul Fleuranges said, “The message to our customers is clear: If you drop something on the tracks, do not attempt to retrieve it. Alert a transit employee or a police officer.”

Meanwhile, cops were investigating a separate incident in which a 50 year-old man was struck and killed by an eastbound No. 3 train at the Utica Avenue station in Brooklyn.

Additional reporting by Tom Namako, Reuven Fenton and Chuck Bennett

todd.venezia@nypost.com

