Eagle-eyed subway riders at a Queens station spotted what looked like a gun on the tracks Wednesday morning triggering an hour-long power shutdown on the F Line to allow cops to grab it, authorities said.

The scramble began at 9:30 a.m. at the 21st St.-Queensbridge station, where straphangers on the platform reported seeing a possible gun on the Brooklyn-bound tracks, authorities said.

NYC Transit cut power to the tracks, allowing cops to gingerly pick up what appeared to be a firearm.

Police were determining whether the weapon was the real deal or a toy, authorities said.

Power was restored to the tracks by 10:30 a.m., cops said.

But the retrieval expedition scrambled service on the busy line, forcing southbound F trains to stop along the M line from Jackson Heights Roosevelt Ave. to 47th-50th Sts.-Rockefeller Center.

A transit alert warned of delays on the F, M and R trains.