The thief, who was caught on camera, allegedly stole the crowns, worth $650 each, from an unlocked ark where they are strored in the basement of Young Israel of Queens Valley on 77th street in Kew Gardens Hills.
The bandit, seen on tape wearing a white T-shirt, grey pants and a black yarmulke, struck while the congregation was in the middle of service upstairs, according to synagogue officials.
The suspect can be seen on surveillance video entering the synagogue, where he picked up a prayer book to to blend in with the crowd.
He then allegedly snuck into the ark and walked out with the crowns, which adorn the sacred scrolls, in a white plastic bag.
The synagogue realized that the crowns were missing on Saturday morning, said administrator Rosayln Ungar.
Anyone with information is asked to call Crime Stoppers at (800)-577-TIPS.