The draft does not explicitly say that a crippling cyberattack against the United States would be among the extreme circumstances. But experts called a cyberattack one of the most efficient ways to paralyze systems like the power grid, cellphone networks and the backbone of the internet without using nuclear weapons.

“In 2001, we struggled with how to establish deterrence for terrorism because terrorists don’t have populations or territory to hold at risk. Cyber poses a similar quandary,” said Kori Schake, a senior National Security Council and State Department official during President George W. Bush’s administration, who is now the deputy director general of the International Institute for Strategic Studies in London.

“So if cyber can cause physical malfunction of major infrastructure resulting in deaths,” Ms. Schake said, the Pentagon has now found a way “to establish a deterrent dynamic.”

The draft review also cites “particular concern” about “expanding threats in space and cyberspace” to the command-and-control systems of the American nuclear arsenal that the review identifies as a “legacy of the Cold War.” It was the latest warning in a growing chorus that the nuclear response networks could themselves be disabled or fed false data in a cyberattack.

So far, all of the United States’ leading adversaries — including Russia, China, North Korea and Iran — have stopped well short of the kind of cyberattacks that could prompt a larger, and more violent response.

The Russians have placed malware called “Black Energy” in American utility systems, but never tried to cause a major blackout. They have sent cable-cutting submarines along the path of undersea fiber optic lines that connect the continents, but not cut them. North Korea has attacked companies like Sony, and used cyberweapons to cause chaos in the British health care system, but never directly taken on the United States.

Still, the document recognizes that American, Russian and Chinese strategies have all been updated in recent years to reflect the reality that any conflict would begin with a lightning strike on space and communications systems. During the Obama administration, for example, a secret program, code-named “Nitro Zeus,” called for a blinding cyberattack on Iran in the event negotiations over its nuclear program failed and Washington found itself going to war with Tehran.