As he has done before, Santorum criticized Casey's work ethic, saying his Democratic opponent has failed to show up for work and has not been a diligent treasurer in failing to change investment policies.
The third-ranking Republican in the Senate said preventing terrorists from getting funding was an essential part of combating terrorism.
"I'm the one trying to fight this war politically and economically so we don't have to fight it militarily, and he is asleep at the switch because he's not doing his job," Santorum said.
Casey's campaign disputed the allegations, calling them a sign of desperation. Santorum has trailed Democrat Casey for months in independent polls.
"This is yet another case of Rick Santorum launching attacks without having his facts straight," Casey spokesman Larry Smar. "Bob Casey has been proactive to try to make sure Pennsylvania taxpayer money is not invested in countries and companies that do business with terror-sponsoring countries."
Santorum did not cite specific examples but referred to a report by the Center for Security Policy, a conservative think tank that has pushed for divestment from companies doing business in terror-sponsoring nations.
"Bob Casey has invested Pennsylvania pension funds in companies with ties to terrorist-sponsoring states and states that engage in genocide," Santorum said. "Bob Casey is aiding and abetting terrorism and genocide."
Casey has called on investment managers to assess whether any companies in their holdings have business in terrorist-sponsoring countries, Smar said. The issue is one facing treasurers across the country.
"Instead of making each state do homework, perhaps the federal government could make it a lot easier" by releasing a list of companies involved with terrorist nations, Smar said.
Santorum said it is not the federal government's place to release a list.
"You have layers of folks who look at, well, you know, are we going to offend our allies? You have the State Department sticking their nose in, you might have the Commerce Department sticking their nose in. There may be all sorts of interests that come into play that can color the picture," he said.
Santorum appeared at a news conference with Missouri state Treasurer Sarah Steelman, who has tackled the investment issue.
Missouri has hired a private company to screen investments, which Santorum said he favored.
Santorum also criticized Casey for not releasing information on where the treasury department is investing money.
The department is in the process of complying with a complicated "fishing expedition" filed by Santorum's campaign, Smar said. Investments are complicated and can change daily, he said.
Each candidate spent part of yesterday privately visiting churches around Pittsburgh. Casey also appeared at a rally in Erie.
"I think he's for the working people," said Tom Trott, 53, truck driver and Teamster, who was one of nearly 200 people at the Erie Maennerchor Club rally.
Trott said Casey was concerned with issues facing workers, such as benefits and preserving Social Security, while Santorum "seems to be about against just about everything we stand for."