Orlando, Fla. ? Americans are increasingly worried that terrorists could launch cyberattacks against banks, transportation networks and other critical systems, a new survey shows.

And technology experts say those fears are grounded in reality.

“I think there is an 80 percent probability we could see an attack in the next two years,” said Paul Henry, vice president of CyberGuard Corp., an Internet security firm based in Fort Lauderdale, Fla.

“We know the expertise is out there among hackers and terrorists. It’s simply a question of the will of terrorists to launch an attack.”

One in two adults expressed concern about the vulnerability of national infrastructure to terrorist hackers in a poll conducted by the Pew Internet & American Life Project and released Sunday.

The poll of 1,001 adults was taken in early August, before the recent power blackout and plague of Internet bugs that disrupted e-mail communications.

“I think the wariness and anxiety we found would be even higher if we had been in the field during those events,” Pew Director Lee Rainie said. “This is such a wired, networked world, people just expect everything to work. We are hardly aware of how dependent we are until something fails and all hell breaks loose.”

Timing aside, concerns about attacks by Web-savvy terrorists shouldn’t be discounted, said several tech experts.

Henry suggested terrorists could launch a double-barreled assault, combining physical destruction such as a bomb blast on a building with a computer attack on a nearby drawbridge, making it difficult for emergency officials to raise the bridge and respond.