The 21-year-old victim got off the subway with several bags at the Bedford Avenue and Nostrand Avenue stop in Crown Heights at about 9:30 p.m. last Thursday, police say.
The suspect saw the woman struggling with the bags and offered to help her get them up the stairs.
The woman accepted the offer and the suspect began helping her carry the bags up to the street. While the two were hauling the bags up the stairs, police say the suspect tried to rape the woman.
The victim screamed and the suspect fled, police say.
The suspect is described as being about 25 to 30 years old, 5 feet 9 inches tall and 150 to 160 pounds.
Anyone with information about the attempted rape is asked to call the NYPD's Crime Stoppers Hotline at 800-577-TIPS.