Putra said officers also found two small plastic packs containing 4.8 grams (.17 ounce) of methamphetamine at Bitar's house.
The arrest was based on a tip-off from nearby residents who suspected that a foreigner was making drug transactions in the area, Putra said.
“We are still investigating how the suspect got those weapons and drugs,” he told reporters at a news conference. “No firearms are allowed in Bali.”
Bitar faces a possible death penalty if found guilty of possessing illegal weapons and drugs, Putra said.
Monday’s arrest is the second for Bitar in Bali. Putra said he was arrested on the island in 2014 with 3.14 grams (.11 ounce) of cocaine in his pocket and sentenced to four months in jail after he was able to convince the judges that the cocaine was only for his own use.
Indonesia has extremely strict firearms and drug laws, and convicted smugglers are often executed. More than 140 people are on death row, mostly for drug crimes. About a third of them are foreigners.