WASHINGTON — The Homeland Security Department wants to buy more than 1.6 billion rounds of ammunition in the next four or five years. It says it needs them — about the equivalent of five cartridges for every person in the United States — for law enforcement agents in training and on duty.

Published federal notices about the ammo buy have agitated conspiracy theorists since the fall. That’s when conservative radio host Alex Jones spoke of an “arms race against the American people” and said the government was “gearing up for total collapse, they’re gearing up for huge wars.”

The government’s explanation is less sinister. Federal solicitations to buy the ammo are known as “strategic sourcing contracts,” which help the government get a low price for a big purchase, says Peggy Dixon, spokeswoman for the Federal Law Enforcement Training Center in Glynco, Ga. The training center and others like it run by the Homeland Security Department use as many as 15 million rounds every year, mostly on shooting ranges and in training exercises.