A former top homeland security adviser to President Bush will tell Congress on Wednesday that chemical plants (search) in the United States are vulnerable terror targets and represent a grave risk to Americans because of weak governmental regulation, FOX News has confirmed.

Richard Falkenrath (search), who left the White House in May, says in a written statement he expects to deliver to Congress that he bears some responsibility for the Bush administration's policy on chemical plant security.

"Regretfully, some portion of this responsibility clearly belongs to me," Falkenrath, now a visiting fellow for foreign policy studies at The Brookings Institution, says in testimony to the Senate Committee on Homeland Security and Governmental Affairs. He gave the remarks to USA Today.

Other witnesses include John Stephenson, director of natural resources and environment at the Government Accountability Office; Stephen Flynn, a senior fellow in national security studies at the Council on Foreign Relations; and Carolyn Merritt (search), the Bush-appointed head of the Chemical Safety and Hazard Investigation Board (search), which probes deadly accidents. Sen. Jon Corzine, D-N.J., will also testify.

Sen. Susan Collins, R-Maine, who is chairing the hearing along with ranking Democratic Sen. Joe Lieberman of Connecticut, told FOX News that chemical plants are one of the nation's most vulnerable targets.

"The problem is that there is no comprehensive federal approach to securing chemical facilities across the U.S. There is very little federal oversight," Collins said, adding that homeland security experts believe chemical plants are "tempting targets" for terrorists.

The government estimates that more than 15,000 chemical facilities are located nationwide, including more than 100 in heavily populated areas. About 160 are earmarked as particularly worrisome because they are so vulnerable to a terrorist attack. Such plants can store enough deadly chemicals to kill or injure hundreds of thousands of people.

Falkenrath is among a growing number of officials rethinking the government's policy to count on chemical plants to beef up their own security voluntarily. Homeland security officials told FOX News that they are not waiting for legislation. Homeland Security Department spokeswoman Michelle Petrovich said inspectors have reviewed security at more than 160 of the 300 plants "of immediate concern."

They are helping the most vulnerable shore up security through federal grant programs.

The bottom line is that DHS has no legal authority to force plants to ramp up security. Wednesday's hearing will examine the adequacy of the industry's response plans as well as those of the government and first responders (search).

One complaint heard by lawmakers is that too much time and money have been spent responding to aviation security as a result of the Sept. 11, 2001, attacks. Not enough has been done to thwart potentially devastating attacks on chemical sites.

The issue took on urgency in January after a rail car derailed in Graniteville, S.C., killing 10 people after several tons of chlorine were released. If a similar incident had happened in a densely populated area, experts say thousands could have been poisoned and killed.

More than three years after the Sept. 11 attacks, Falkenrath will tell the Senate committee that chemical plants and rail cars (search) that transport deadly chemicals continue to be easy, unprotected targets for terrorists.

Recently, a federal court upheld a Washington city ordinance banning rail shipments of toxic chemicals through the nation's capital after reviewing evidence that a terrorist attack on such a train could kill 100,000 people.

Merritt, who has never before spoken publicly about chemical security, said she will tell the committee that the federal government needs to do more to protect the public from the intentional or accidental release of deadly chemicals, USA Today reported.

Merritt's testimony, which she provided to the newspaper, says there are "serious gaps in the preparations for major chemical releases by companies, emergency responders, government authorities and the public."

In his testimony, Falkenrath urges Congress to require the Homeland Security Department to maintain an inventory of chemical plants, develop safety standards, verify that plants have met those requirements and impose civil and criminal penalties on those that fail.

Even the American Chemistry Council, which represents companies accounting for 90 percent of the nation's industrial chemical production, favors government regulation to "level the playing field" by requiring all plants to pay for security upgrades, council spokeswoman Kate McGloon told USA Today.

FOX News' Catherine Herridge contributed to this report.