* U.S. sees power grid as vulnerable to cyber-attacks
* White House leading review of cyber-security
* Chinese are "all over the place," former official says (Updates throughout)
WASHINGTON, April 8 (Reuters) - U.S. concerns about the potential for cyber-attacks on critical infrastructure extended to the American electrical power grid on Wednesday and experts pointed the finger anew at Chinese hackers, among others.
As a result, electric utilities are likely to face new pressures from the U.S. Congress and government regulators to tighten security and preparations against computer intrusions that would wreak widespread havoc.
U.S. Homeland Security Secretary Janet Napolitano told reporters the power grid is vulnerable to potentially disabling computer attacks, while declining to comment on reports that an intrusion had taken place.
"The vulnerability is something that the Department of Homeland Security and the energy sector have known about for years," she said. "We acknowledge that ... in this world, in an increasingly cyber world, these are increasing risks."
Napolitano spoke after The Wall Street Journal reported that cyber-spies had penetrated the U.S. electrical grid and left behind software programs that could be used to disrupt the system.
The Journal said the intruders have not sought to damage the power grid or other key infrastructure but could try during a crisis or war.
The United States for several years has accused the Chinese and Russians, among others, of using cyber-attacks to try to steal American trade secrets, military secrets and government secrets.
James Lewis, cyber-security analyst at the Center for Strategic and International Studies, said Russia and China have long been considered culprits in computer spying and that the United States, France and Germany have all complained to China in particular.
"In four out of five cases we really can't be sure who's doing it but in the (other) 20 percent it points very often to China and Russia."
A former U.S. security official told Reuters that the Chinese have been particularly active.
"They are all over the place," said the official, who spoke on condition of anonymity. "They're getting into university systems, contractor systems, hacking government systems. There's no reason to think that the electrical system would be immune as well."
Eric Rosenbach, executive director for research at Harvard University's Kennedy School of Government's Belfer Center, said that if true, it showed that the Chinese and Russians are thinking strategically about how to either constrain the United States or inflict more damage if they ever felt they needed to do so.
"I think that China recognizes if in a very strategic sense you want to ensure you have the ability to exploit another country's potential weakness or vulnerability but do it in a way that isn't confrontational or cause an international crisis, then this is a very good way of doing that," he said.
President Barack Obama, aware of the concerns about the vulnerability of infrastructure, has launched a cyber-review that is expected to be completed in the coming weeks.
White House spokesman Nick Shapiro said the White House was not aware of "any disruptions to the power grid caused by deliberate cyber-activity here in the United States."
"The Department of Homeland Security works with industry to identify vulnerabilities and to help industry enhance the security of control system networks. The federal government is also working to ensure that security is built in as we develop the next generation of 'smart grid' networks," Shapiro said.
Mississippi Democratic Representative Bennie Thompson, chairman of the House of Representatives Homeland Security Committee, said he would introduce legislation to address the grid's vulnerability to cyber-attack.
"Our electric system is critical to our way of life,and we cannot afford to leave it vulnerable to attack," he said. "Our oversight indicates there is a significant gap in current regulation to effectively secure this infrastructure."
The United States is not alone. CIA analyst Tom Donahue told a power-industry conference last year that "we have information from multiple regions outside the United States, of cyber-intrusion into utilities followed by extortion demands."
The North American Electric Reliability Corp, the industry group with responsibility for grid reliability and security for the United States and Canada, said it was unaware of any cyber-attacks that have led to disruptions of electric service. The group has been working for several years with the industry to create and implement cyber-security measures.
American Electric Power Co (AEP.N) spokeswoman Melissa McHenry said the utility long ago identified "numerous scans and probes of our networks from external sources" and had put in place a multilayered security system.
Still, she said, "We realize that there are no guarantees that you can always be completely safe from a cyber-attack. We continually monitor the effectiveness of our systems and seek to enhance them." (Additional reporting by David Alexander in Washington, Michael Erman in New York and Eileen O'Grady in Houston; Editing by Will Dunham and Bill Trott)