Two immigrants charged with plotting to blow up a Riverdale synagogue will face more than 30 years in jail if convicted — but not life, authorities said yesterday.

Ahmed Ferhani and Mohamed Mamdouh pleaded not guilty to lesser state charges including criminal possession of a weapon as a terror crime in a scheme to blow up city synagogues.

But a grand jury rejected the initial top charge against the pair, second-degree conspiracy as a terror crime, which carried the potential for life in prison.

The top charges now, including the weapons count, are punishable by up to 32 years behind bars; the men also still face a less serious terror conspiracy count and hate-crime counts.

Ferhani and Mamdouh were arrested on May 11 on charges they wanted to strike a synagogue to avenge “mistreatment” of Muslims around the world.

Wiretap recordings caught the men calling Jews “rats” and other names.