Several health and environmental groups are urging U.S. Sen. Susan Collins of Maine to support federal legislation that the organizations claim will help close a dangerous hole in U.S. anti-terrorism policies.

The groups are pushing for Congress to enact legislation that would require facilities that use certain highly toxic chemicals to switch to safer alternatives whenever economically and technically feasible.

The bill, titled the “Chemical Facility Anti-Terrorism Act of 2008,” targets only facilities where a terrorist attack poses the highest risk of widespread injury or death to nearby population centers. Those chemicals include chlorine, ammonia, sulfur dioxide and hydrogen fluoride.

On Wednesday, members of the Environmental Health Strategy Center, Greenpeace and the Maine People’ s Alliance delivered more than 10,000 postcards to Collins’ office in Bangor. The postcards, which were distributed to Greenpeace members throughout the country to sign and mail back, urge Collins not only to support the bill but also to rally support from key Republican colleagues.

“We are counting on Senator Collins to be a leader,” said Mike Belliveau, executive director of the Environmental Health Strategy Center. “Congress does need to finish the job and there is still time to finish the job this session. Literally, the lives and health of millions of Americans depend on this.”

As ranking member of the Senate Committee on Homeland Security and Governmental Affairs, Collins is one of the most influential senators in determining whether the legislation succeeds, Belliveau said.

Jen Burita, a spokeswoman for Collins, pointed out in an e-mail that the petitions submitted Wednesday pertain to a House bill that has not been voted on by the full House and has yet to come before the Senate.

Burita wrote that Collins spearheaded legislation enacted by the last Congress that significantly strengthens security at chemical facilities. The legislation, for the first time, gave the Department of Homeland Security the authority to shut down unsafe facilities.

The current House bill, HR 5577, passed the House Homeland Security Committee in March.

Congress has debated several chemical security bills since the September 2001 terrorist attacks. A temporary measure passed in 2006 is set to expire soon. The chemical industry and some Republican leaders have advocated making the temporary rules permanent.

But some health and security experts have argued that communities located near chemical facilities or rail lines used to transport toxic chemicals need additional protections from terrorist attack. Specifically, they want the federal government to require high-risk facilities to switch to safer alternatives.

One example would be trading pure liquid chlorine, which can gasify into a deadly mist when released from a ruptured tank, for less-toxic liquid chlorine bleach or ultraviolet technology to disinfect water.

According to the Congressional Research Service, there are nearly 7,400 facilities in the United States in which at least 1,000 people would be at risk from a “worst-case release” of chemicals. Eighteen of those facilities are in Maine.