Screenshot by CNET

The US Intelligence Community -- including the National Security Agency and 15 other government agencies -- may be carrying on with essential duties during the government shutdown, but one source says 70 percent of the IC's civilian workforce has been sent home, and staff reductions have caused concern at the Office of the Director of National Intelligence.

As noted in a memo (PDF) from the Defense Department, intelligence and surveillance "required to support national or military requirements necessary for national security" are among the "missions and functions of the Department of Defense that may continue to be carried out in the absence of available appropriations."

However, the memo says, "only the minimum number of civilian employees necessary to carry out excepted activities will be excepted from furlough."

That means the NSA and other such outfits aren't running at their usual strength (one source within the intelligence community told CNET that 70 percent of the IC's civilian workforce is now out on furlough). That decrease in workers apparently makes the Office of the Director of National Intelligence somewhat uneasy.

"The Intelligence Community's ability to identify threats and provide information for a broad set of national security decisions will be diminished for the duration," Shawn Turner, director of public affairs for National Intelligence, said in a statement. Turner continued:

The immediate and significant reduction in employees on the job means that we will assume greater risk and our ability to support emerging intelligence requirements will be curtailed. The fraction of Intelligence Community employees who remain on the job will be stretched to the limit and forced to focus only on the most critical security needs.

U.S. Defense Secretary Chuck Hagel seems to agree. In general comments about the shutdown's effect on civilian workers in the Defense Department, Hagel told a group of reporters in Seoul on Tuesday: "When you take that number of civilian employees out of the mix of everyday planning and working...you're going to impact readiness. There's no point in kidding about that. But [Americans] should not be concerned that their security is now in jeopardy. It is not; it will not be."

Of course, critics of the scope of the NSA's surveillance efforts -- which have been in the spotlight since former contractor Edward Snowden leaked top secret internal documents to journalists -- might counter that such a slimming of the shadowy agency's activities is long overdue.

Regardless, the remarks from Turner and Hagel seem to make it plain that it's not just tourist access to monuments like the Statue of Liberty -- or the continued operation of government Twitter accounts -- that's being affected by Congress' inability to come to terms on a federal budget.