WASHINGTON – Two deadly railroad accidents in the past month have sparked new debate about the government’s efforts to secure the nation’s rail system and ensure that such accidents do not provide new opportunities for terrorists who might seek to use railroad cars as weapons.

In Graniteville, S.C., a train carrying hazardous materials derailed near a switchyard, causing a green cloud of chlorine to leak. The accident killed nine, the deadliest such crash in more than 20 years, and prompted hundreds of people to be evacuated from their homes for days.

On Wednesday, a suicidal man parked his vehicle on the tracks in California, causing a multi-train accident, killing 11 and injuring 200. Juan Manuel Alvarez, 25, who is charged with murder in that incident, appeared in court Friday, but the hearing was delayed so he could undergo further medical evaluation.

Even though the accidents do not show any signs of involving terrorism, elected leaders and safety officials said they point to long-known safety problems in the rail system that could be exploited by terrorists. Each year, at least one or two derailments of trains carrying hazardous material prompt an evacuation of an entire town. There are about 300 fatalities each year from vehicle collisions at grade crossings, according to the Federal Railroad Administration, although they usually do not cause a derailment.

“This is very similar to what we saw happen with aviation security” before the terrorist attacks in 2001, said Jim Hall, former chairman of the National Transportation Safety Board. “Only that instead of airports, we have a nation that is crisscrossed with railroad tracks. We’ve got to put additional resources in terms of looking at … the weak links.”

One example, Hall said, is that railroads could install better surveillance technology to alert them to a vehicle parked on a railroad track, such as the one that caused Wednesday’s accident. Safety officials have also long urged better maintenance of rail tracks, particularly those running through tunnels. In July 2001, a train derailed in the Howard Street tunnel in Baltimore. One of the cars contained the hazardous material tripropylene, which fueled a massive fire that forced the evacuation of Camden Yards baseball park and cost $12 million to clean up.

The Federal Railroad Administration said it has taken steps to improve safety, such as recently warning about the need to better monitor rail switches after the Graniteville accident. Part of the challenge of security, rail experts say, is that there are so many thousands of miles of track and it is difficult to protect them from threats without slowing down commerce.

Since the 2001 terrorist attacks, the railroad industry says it has started programs to improve security, such as one that trains railroad employees to look for unusual or suspicious activity and report it on toll-free hotlines. The Department of Homeland Security has proposed removing hazmat signs on trucks and rail cars carrying hazardous materials, so that terrorists will not be able to target them. The Transportation Security Administration has also run test programs at passenger train stations to screen passengers on commuter trains for explosive residue.

But the effort has been slow going. The TSA, which is in charge of rail security, spent so much time on airline security that it had not developed a plan to protect the rails from a terrorist attack as of 2003, according to a report by the General Accountability Office. TSA has since directed rail operators to develop security programs to the agency’s standards.

TSA officials say they plan to use explosive detection machines at rail stations only during major public events, such as the inauguration earlier this month. TSA has not decided yet about removing the hazmat signs, after safety and some industry officials objected that it would hamper emergency responders efforts to protect themselves and treat victims in the event of an accident.

Jonathan Fleming, TSA’s chief operating officer, said most of the rail security work has been behind the scenes. “We didn’t take over security operations in rail the same way we did in aviation, so it may look different,” Fleming said. “It might not be as visible or as sexy, but we’ve certainly been working on it since the early days.”

Railroad workers regularly report suspicious incidents, according to one major railroad executive, but most of them turn out to be nothing. “It would not be difficult at all to blow something up,” said the executive, who spoke on the condition of anonymity because the executive is not authorized to speak on security matters. “The one in South Carolina was an accident. You could recreate those circumstances pretty easily.”

Security experts said it is difficult to know how seriously terrorists might be considering targeting rail because it has not happened in this country in recent memory and the rail lines are not as symbolic a target as they are in Europe.

“There is a lot of unpredictability” in targeting rail cars with hazardous material, said Jack Riley, a security expert at Rand Corp. “The wind conditions have to be right, and even with that if you don’t breach the container in just the right way, you might not get the contamination you might be seeking.”