A Falls Church man hailed as a hero for trying to save a teenager’s life during a powerful storm in June has been charged by Montgomery County police with soliciting sex with a minor.

Nathan S. Portnoy, who was credited with pulling Dylan S. Cooper away from a downed power line and trying to revive him during the June 29 derecho, faces kidnapping and first-degree assault charges after attempting to begin a sexual relationship with a 12-year-old Bethesda girl, police said.

Using the Internet and the telephone, Portnoy, 23, of Emilys Lane, carried on a three-month relationship with the girl, who portrayed herself as an adult, police said. After several conversations about having sex, Portnoy and the girl arranged to meet Aug. 24 about 5:30 p.m. in a park near the girl’s home, police said.

Police said that after playing soccer with the girl, Portnoy invited her to dinner. But after traveling a short distance in his vehicle, the girl asked to get out. Members of her family, who were in the area, saw her exiting the vehicle and followed it. Police said Portnoy pointed a gun at them through the rear window and the family summoned help.

Police arrested Portnoy Aug. 25 in his vehicle, which was seized. A search of the vehicle turned up a loaded handgun, ammunition, gun holsters, handcuffs, “zip ties,” rope, a black ski mask, and several boxes of condoms, police said. He has been charged with first-degree assault, kidnapping a child under 16 and sexual solicitation of a minor.