WASHINGTON — Starting Friday, chemical companies, railroads, electric utilities and other parts of the nation’s critical infrastructure can begin submitting sensitive information to the Department of Homeland Security about their vulnerabilities to terrorist attacks with assurances that their proprietary data would be safe from public disclosure.

Under the Homeland Security Act of 2002, the department can deem data voluntarily provided by businesses that help the government stave off possible disruptions by terrorists as secret and unavailable to outsiders. The law’s supporters view it as a way for U.S. officials to help map security plans for critical U.S. infrastructure, 85 percent of which is in private hands.

But some advocates for environmental-protection and open-records laws say unscrupulous firms might manipulate the rules as part of an attempt to evade federal enforcement of health or safety rules.

Sean Moulton, a senior policy analyst with OMB Watch, a nonprofit group that opposes government secrecy, said that during the drafting of the law and the rules being released this week, key industries successfully lobbied for procedures ensuring that any information they share with Homeland Security would remain secret and would not be useable by other agencies in civil enforcement actions.

"The government agreed that ‘we’ll keep secret this information you give to Homeland Security, and we won’t do anything with it,’ " other than for counterterrorist purposes, Moulton said. "It’s naive to think we won’t have bad actors in industry" misusing the protections.

Federal officials said they will strive to prevent the rules from allowing firms to avoid accountability for wrongdoing by including data about, for example, pollution at a chemical plant in a confidential report to the Homeland Security Department about security gaps.

Robert Liscouski, the department’s chief of infrastructure protection, said his staff will strive to ensure that the law is "not providing a safe haven" for corporate wrongdoers. Companies can be charged with felonies if they mislead the department into believing that the data they provide are not related to any enforcement matters being considered by other agencies, officials said.

U.S. officials have no power under the Homeland Security Act to compel industries to provide data about their security gaps, so any corporate cooperation would be voluntary.

Safeguarding nuclear plants, telecommunications nodes and thousands of other critical networks was one of the main reasons for the formation of the Homeland Security Department last year. It is an arena in which it is critical that U.S. officials synchronize their efforts with private industry, officials said.

U.S. officials found soon after the Sept. 11, 2001, attacks that many industries were reluctant to share information about their operations and their security vulnerabilities because of fears of legal liability and concern that the information would be unearthed by outsiders using the federal Freedom of Information Act.