WASHINGTON — The federal government spent more than $11 billion to protect its secrets last year, double the cost of classification a decade ago — and that is only the part it will reveal. The total does not include the costs incurred by the Central Intelligence Agency, the National Security Agency and other spy agencies, whose spending is — you guessed it — classified.

John P. Fitzpatrick, head of the Information Security Oversight Office, which oversees the government’s classification effort and released the annual report, said that adding the excluded agencies would increase the spending total by “less than 20 percent.” That suggests that the real total may be about $13 billion, more than the entire annual budget of the Environmental Protection Agency.

The costs include investigations of people applying for security clearances, equipment like safes and special computer gear, training for government personnel, and salaries for officials who review documents for classification and declassification.

Spending on secrecy has increased steadily for more than a decade, driven in part by the expanding counterterrorism programs after the 2001 terrorist attacks, but also by the continuing protection of cold war secrets dating back decades. The total cost for 2001 was $4.7 billion, the oversight office said.