In a shootout with 23 officers from seven different agencies, he said, “law enforcement fired approximately 380 rounds at the suspects.” During the shootout, a San Bernardino officer was shot in the leg and a sheriff’s deputy was cut by flying debris.

Most of the carnage unfolded in a single room of the Inland Regional Center, which provides services to people with disabilities and was filled with people Mr. Farook knew, the police said. While shots rang out, others in the building cowered and hid, sending text messages or making frantic calls.

The suspects were armed with two .223-caliber assault rifles and two 9-millimeter semiautomatic pistols — all obtained legally — and they left behind at the center an explosive that did not detonate, made of three pipe bombs, Chief Burguan said.

In a rented Ford Expedition with Utah plates, he said, the couple had 1,400 rounds for the rifles and 200 for the handguns with them at the time of the shootout. And at the small duplex townhouse where they apparently lived in the nearby city of Redlands, officers found more than 2,500 rounds for the assault rifles, more than 2,000 for the pistols, several hundred for a .22-caliber rifle, and 12 pipe bombs. There were also supplies for making more bombs.