"What I think we really need to be concerned about is when these (attacks) transition from disruptive to destructive," General Alexander said in a speech at the American Enterprise Institute, a Washington think tank.
Critics say such a law would erode civil liberties by allowing firms to onpass private data.
General Alexander, who also heads the US Cyber Command, sought to calm fears about privacy breaches.
"For situational awareness, we need to be able to see what's going on. I don't mean the government has to be in the network to see," he said.
"Like the police force, like the fire department, they don't see around buildings waiting for a fire to come on, you call them when it happens. In cyberspace, I see very much the same thing in our partnership with industry."
There is no need for the government to read personal emails, he said, assuring the audience that the NSA doesn't "hold data on American citizens."
Source: agencies
