The Homeland Security Department is wasting time and money on its current plan to develop technology to detect nuclear material at the nation's borders, two senators said Wednesday.

Sens. Joseph Lieberman, I-Conn., and Susan Collins, R-Maine, slammed the department for not having a strategic plan to develop critical technology that could prevent a nuclear terrorist attack on the U.S.

Congressional investigators have criticized the program since 2006. The Obama administration blames most of the program's problems on the Bush administration. But Lieberman and Collins say the current administration isn't working fast enough to fix them.

"We're not happy or satisfied with progress on the whole nuclear detection architecture," Lieberman said.

The department has spent $400 million to develop two technology programs that have failed and $4 billion to develop nuclear detection technology over the past seven years. Lawmakers and congressional investigators have repeatedly criticized those efforts, saying the department has little to demonstrate that the cost justifies the programs.

Homeland Security Deputy Secretary Jane Holl Lute said Wednesday that the department is improving the technology program.

"We are mindful of getting something delivered that has a credible basis for the implementation plan that follows," Lute said during a hearing before the Senate Homeland and Governmental Affairs committee.