The U.S. Park Police has lost track of a huge supply of handguns, rifles and shotguns, according to a report released Thursday on the law enforcement agency responsible for safeguarding the National Mall and critical American landmarks.

In the scathing report, the inspector general's office of the Department of Interior faults staff at the agency for having no idea how many weapons they control and says the department has no clear policies or procedures for investigating missing weapons. The office said top managers, including the police chief, have shown a "lackadaisical attitude toward firearms management."

"Historical evidence indicates that this indifference is a product of years of inattention to administrative detail and management principles," deputy inspector general Mary Kendall wrote to Jonathan Jarvis, the director of the National Park Service, in a letter that accompanies the report.

While surveying Park Police field office armories, investigators found more than 1,400 extra and unassigned weapons that were intended to be destroyed. They also found 198 handguns that were transferred from the Bureau of Alcohol, Tobacco, Firearms and Explosives and stored in an operations facility firearms room without being recorded in an inventory system.

Investigators also found that an officer who had been detailed to President Obama's inauguration in January retained a semi-automatic rifle without permission and stored it at his home. Another officer stored a shotgun at his home in San Francisco without permission, according to the report.

"We found credible evidence of conditions that would allow for theft and misuse of firearms, and the ability to conceal the fact if weapons were missing," Kendall wrote.

The report, which was first reported by The Washington Post, concluded that the agency failed to fully investigate weapons it could not account for, including 18 pistols, shotguns, and rifles that were entered into a national database as missing or stolen.

As recently as April 2013, two automatic rifles were discovered during a firearms search at the agency's aviation unit for which officials had no prior knowledge, the report states.

The watchdog agency said its report was triggered by an anonymous tip suggesting that the Park Police could not account for government-issued military-style weapons.

A spokesman for the agency did not immediately return an email seeking comment, and an evening shift commander said he hadn't seen the report and couldn't discuss it.

The report also includes 10 recommendations to improve firearms management.

The Associated Press contributed to this report.