Holly Harrington, a spokeswoman, said the agency is not sure exactly how long it will stay open, but it should be able to operate for at least a short period using unspent money from previous years.

The National Oceanic and Atmospheric Administration, based in Silver Spring, will lose about half of its staff in the face of a shutdown. According to a recent Commerce Department document outlining its shutdown plan, roughly 6,600 NOAA employees would stay on the job.

Most of those workers would come from the National Weather Service, which is required to continue functioning because its work can identify "imminent threats to protect life and property." In addition, about 500 employees from the National Marine Fisheries Service, which regulates and enforces laws related to marine wildlife, would also stay on the job.

However, even with those exceptions, approximately 5,400 NOAA employees — about 45 percent of the agency's workforce — would be sent home.

Another Silver Spring-based agency, the Food and Drug Administration, will furlough about 8,000, or 45 percent, of its 14,779-person workforce. With those sorts of cuts, the agency says it "will be unable to support the majority of its food safety, nutrition, and cosmetics activities."

Some of those halted activities include routine establishment inspections and monitoring U.S. imports.

The National Institutes of Health, based in Bethesda, will not be accepting new patients nor will it be taking on new clinical trials, extramural research grants or contracts. Without admitting new patients, NIH will be carrying on with roughly 90 percent of its normal patient load during the shutdown.

NIH will also be keeping employees who protect property related to ongoing medical experiments, maintenance of animals and protection of government-owned property.

According to its contingency plan, "For some of the on-going experiments, a break in the protocol would render the research property (both animate and inanimate) useless and require some of it to be destroyed. "

In total, NIH will keep about 27 percent of its 18,646-person staff.

NASA's Goddard Space Flight Center in Greenbelt will retain 104 of its 3,397 federal employees in the wake of a government shutdown, with only 60 of those employees full time. That will leave the center with a bare bones staff only three percent of its normal size. Goddard will also have 251 employees who are "on-call," meaning they will only come to the center if there is an emergency.

Small effect on the Bay

Government funds also play a role protecting the Chesapeake Bay watershed, and with the EPA expected to lose 94 percent of its employees, according to its 2013 contingency plan, Chesapeake programs are expected to lose some of their workforce.

However, Margaret Enloe, a spokeswoman for the Chesapeake Bay Program, said that water monitoring and restoration programs should not be affected by the shutdown. She said most of the employees are funded by state programs or partnerships, so they will continue to work even if there is a shutdown.

But she added that those employees, many of whom work at the EPA-owned headquarters in Annapolis, will be seriously inconvenienced.

"There is a physical building that is managed by the EPA, and that building will be closed," Enloe said. Because of that, Enloe said, most employees will not be able to work or meet in the building.

Employees will instead work from home, which Enloe said is frustrating but ultimately easy to deal with.

"I'll give you one example," Enloe said. "We have a giant conference room that we use for meetings, and if the government shuts down, we can't use it. But then you go find another place or have a conference call."

Capital News Service's Joshua Axelrod contributed to this story.