The expansion would increase the Defense Department's Cyber Command by more than 4,000 people, up from the current 900, an unidentified American official said.
"Defense officials acknowledged that a formidable challenge in the growth of the command would be finding, training and holding onto such a large number of qualified people," the New York Times said in a report.
As part of the expansion, officials said the Pentagon was planning three different forces under Cyber Command: "national mission forces" to protect computer systems that support the nation's power grid and critical infrastructure; "combat mission forces" to plan and execute attacks on adversaries; and "cyber protection forces" to secure the Pentagon's computer systems.
The report said the move is part of a push by Defence Secretary Leon Panetta to bolster the Pentagon's cyberoperations.
Defence officials said that Panetta was particularly concerned about a computer attack last August on the state oil company Saudi Aramco, which infected and made useless more than 30,000 computers.
In October, American intelligence officials said they were increasingly convinced that the Saudi attacks originated in Iran.
They described an emerging shadow war of attacks and counterattacks already under way between the US and Iran in cyberspace, the report said.
Iran's cyberwarfare capabilities are "weaker" than those of China and Russia, which intelligence officials believe are the sources of a significant number of attacks on American companies and government agencies.
