The creation of the Department of Homeland Security has left the nation “better prepared” to prevent catastrophic terrorist attacks, but the agency still needs to address “gaps and weaknesses” in its mammoth effort to restructure the federal government, the head of the Government Accountability Office told a Senate committee Wednesday.

The department, created in the wake of the Sept. 11, 2001, attacks, is the third-largest department in the federal government, with more than 200,000 employees and an annual budget of more than $50 billion, and involved the merger of 22 federal agencies.

“Has it worked? Has it made us safer as a nation?” Sen. Susan Collins of Maine, the ranking Republican on the Senate Committee on Homeland Security and Governmental Affairs, asked at Wednesday’s hearing.

“We’re definitely better-prepared as a nation to address these issues,” Gene Dodaro, the GAO comptroller general, said. “The benefits of putting those agencies together are becoming clearer.”

“We have been spared another catastrophic terrorist attack, and I don’t think that is a coincidence,” said Sen. Joseph I. Lieberman (I-Conn.), chairman of the committee and a key supporter of the department’s creation in 2003

The GAO released a new report assessing DHS to mark the 10th anniversary of the attacks. The Washington Post obtained an advance copy.

“Eight years after its creation and 10 years after September 11, 2001, DHS has indeed made significant strides in protecting the nation, but has yet to reach its full potential,” says the report, which credits DHS with “noteworthy accomplishments.”

“The kind of turf protection that went on before was impossible to defend after 9/11,” Collins said.

Management problems have contributed to schedule delays, cost increases and performance problems in major programs, according to the report.

One example cited is the Coast Guard’s Deepwater Program to modernize ships and aircraft, which has faced problems because DHS lacks skilled personnel in fields such as acquisition management, according to the report.

The department’s failure to leverage its buying power has resulted in its paying “billions more” than it should have, Collins noted.

DHS also needs to improve information-sharing with other federal agencies about cyber-based threats, the report states.

“The status quo is not acceptable in the field of cyber-security,” testified Jane Holl Lute, the deputy secretary of the department.

Lieberman warned that significant additional cuts to the DHS budget “could reverse many of the homeland security gains that have been achieved.”

The report credits the department with important advances in its eight years, including the creation of a quadrennial homeland security review to provide a framework for government efforts, and the assumption of security screening responsibilities at airports nationwide.

Staff writer Joe Davidson contributed to this report.