WASHINGTON » Edward J. Snowden’s employer, Booz Allen Hamilton, has become one of the largest and most profitable corporations in the United States almost exclusively by serving a single client: the U.S. government.

Through the past decade, much of the company’s growth has come from selling expertise, technology and manpower to the National Security Agency and other federal intelligence agencies.

The government has sharply increased spending on high-tech intelligence gathering since 2001, and both the Bush and Obama administrations have chosen to rely on private contractors like Booz Allen for much of the resulting work.

Thousands of people once employed by the government, and still approved to deal with classified information, now do essentially the same work for private companies. Snowden is among them. As evidence of the company’s close relationship with government, the Obama administration’s chief intelligence official, James R. Clapper Jr., is a former Booz executive. The official who held that post in the Bush administration, John M. McConnell, now works for Booz.

"The national security apparatus has been more and more privatized and turned over to contractors," said Danielle Brian, executive director of the Project on Government Oversight, a nonprofit group that studies federal government contracting.

Companies like Booz, Lockheed Martin and Computer Sciences Corp. also engage directly in gathering information and providing analysis and advice to government officials. Booz employees work inside the facilities at the NSA, among the most secretive of the intelligence agencies.

The company employs about 25,000 people, almost half of whom hold top-secret security clearances. Booz Allen reported revenues of $5.76 billion for the fiscal year ended in March. The government provided 98 percent of that revenue, the company said.

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