I can't comment on what Chomsky may or may not consider to be a war crime. However, I can point out at least once instance where troops under Carter's command fired shots and killed someone.

In 1979, Iranians took over the US Embassy in Tehran, and took the embassy staff hostage. Carter authorized Operation Eagle Claw, a rescue mission. The operation was launched on the night of April 24, 1980.

Eagle Claw was launched from the USS Nimitz in the Persian Gulf near Chabahar. As this is around 1800km from Tehran, it required multiple stops at predetermined staging areas to refuel. The first staging area was designated Desert One, and was located as close to the middle of nowhere as possible.

Flying in the middle of the night into the middle of the desert, the Americans hoped to land, refuel, and be gone without being spotted. Unfortunately, they were spotted. Two vehicles stumbled upon them that night: a tanker truck, and a bus full of people. The bus was halted with warning shots, and the 44 people inside were held captive. The tanker truck fled instead of halting, so it was destroyed with a shoulder-mounted rocket launcher. One Iranian civilian was killed.

To cover their tracks, the Americans planned to destroy the bus and fake that it had crashed into the tanker truck to cause the explosion. The 44 captives would be dropped back into Iran at a later date, possibly the next night. However, disaster soon struck: a helicopter and a plane collided and exploded, killing 8 Americans. The remaining team evacuated immediately, leaving the 9 bodies and 44 hostages behind.

All this is to say, troops under Carter's personal authorization did fire shots in anger on at least one occasion. One civilian was killed, and 44 were taken captive.

Source: Guests of the Ayatollah by Mark Bowden, 2006