Construction crews prepare a set of border wall prototypes along the U.S. border with Mexico on U.S. Customs and Border Protection property near San Diego, California.

The Trump administration's plan to build its long-promised border wall is "proceeding without key information," including any assessment of costs, according to a government study published Monday.

This shortcoming could waste time and money, according to the study from the Government Accountability Office. "DHS faces an increased risk that the Border Wall System Program will cost more than projected, take longer than planned, or not fully perform as expected," the GAO concluded.

The Department of Homeland Security also failed to document its plans for a section of the proposed barrier in San Diego as required, the report said.

The GAO audit was sparked by a request from Democrat lawmakers Sen. Claire McCaskill of Missouri and Reps. Bennie Thompson of Mississippi and Filemon Vela of Texas.

"To be blunt, this Administration has no clue what it is doing and must be held accountable," Thompson said.

"Simply put, the White House has not done their homework; they are gambling taxpayer money while operating on incomplete information," Vela said in a joint statement with Thompson.

DHS says it concurred with the report's recommendations to analyze the costs of future wall segments and document certain plans. But in a letter to the watchdog office included in the appendix of the report, DHS official Jim Crumpacker pushed back.

"It is misleading and inaccurate for GAO to say that progress is not being documented or to imply that progress is not being tracked," Crumpacker said in the letter.

Crumpacker also disagreed that DHS should analyze costs before looking at operational risks. "There is nothing in the guidance prohibiting an approach that first looks at the operational priorities based on risks/threats," he said.

In a statement to CNBC, a DHS spokeswoman defended the push to build a border wall. "Americans deserve a secure border that protects our communities and keeps America safe and this administration is doing so by constructing the first border wall in a decade," the spokeswoman said.

The department received $1.34 billion for "fencing" along the southern borders of the Rio Grande Valley and San Diego in the latest government spending bill. Trump wanted as much as $25 billion for the border wall and had reportedly proposed funding it through the military.

DHS has requested an additional $1.6 billion for the construction of a "wall system" covering about 65 miles of the Rio Grande Valley sector in the next spending bill, according to the report.