About 58% of federally licensed firearms dealers have not been inspected by the Bureau of Alcohol, Tobacco, Firearms and Explosives in the past five years.

According to a report by the Justice Department's Office of Inspector General, the federal agency that enforces gun laws is stretched too thin to keep up with the growing number of firearms dealers. The result: It often takes more than a year — sometimes more than three years — for the agency to revoke a dealer's license after finding serious violations.

The report found violations of record-keeping rules are up 276% since 2004, but the number of firearms licenses revoked is down 43%.

The number of gun dealers has increased 16% since 2004, and the report found ATF improving in some areas. Although license revocations are down, the number of other enforcement actions, such as warning letters and suspensions, is almost four times higher.

But the agency says it doesn't have the manpower to meet its goal of inspect every dealer at least once every three to five years.

In a formal response, the ATF says shifting resources to routine inspections isn't an option. That's because the law requires the agency to make other issues a priority: inspecting explosives licensees, processing new gun-dealer applications within 60 days and focusing on high-risk gun dealers.

In 2011, 62% of inspections found no violations. Most of the violations the ATF did find were paperwork errors, such as failing to keep updated records, keep a copy of a purchaser's identification or sign and date the required forms. Unless inspectors find multiple violations that would require a reinspection, a 1986 federal law bans the agency from making more than one unannounced inspection every year.