EXPLAINER-What happens when the U.S. federal government shuts down?

(Updates story originally published in September)

By Jason Lange

WASHINGTON, Dec 1 (Reuters) - The U.S. Congress is running out of time to avert a partial government shutdown, which would lead to furloughs for potentially hundreds of thousands of federal workers in the middle of a national health crisis.

Barring a deal https://www.reuters.com/world/us/some-republicans-us-congress-try-close-government-over-vaccine-mandates-2021-12-01, funding for most federal agencies will expire at midnight on Friday. Many government functions would grind to a halt in the second federal shutdown in three years.

Museums and national parks would close and roughly three in five workers - out of a federal civilian workforce of roughly 2.2 million - could be barred from working.

Furloughs could hit 62% of employees at the U.S. Centers for Disease Control, an agency at the center of America's fight against the COVID-19 pandemic, according to an agency shutdown plan.

HOW DOES THIS AFFECT COVID-19 RESPONSE?

Federal workers can stay on the job if being away puts lives or property at risk. But many would have to work without being paid until funding is approved. And those in less critical roles will be furloughed.

The Department of Health and Human Services' shutdown plan pledges the CDC "will continue full support" for public health needs. But the budget headache could still be a distraction.

HOW DOES A SHUTDOWN ACTUALLY HAPPEN?

After funding expires, some workers can clock in briefly to set department shutdowns in motion, such as choosing who would be exempt from furlough and adding a shutdown message to government voice mails.

Shutdown plans in the past have included suspending processing of applications for firearms and passports.

Much of government would continue on autopilot, having no impact on the government's ability to pay bills even as it nears a $28.9 trillion debt limit, said Philip Wallach, an expert on politics and government administration at the American Enterprise Institute, a conservative think tank.

Even with furloughs, the Treasury Department would make debt payments and mail Social Security pension checks. Soldiers could still fight wars, but many civilians in the Department of Defense would be furloughed.

HOW COULD A SHUTDOWN BE AVOIDED, OR KEPT BRIEF?

Congress, which Democrats narrowly control, must pass a spending bill to keep the government from shutting down or to reopen it.

U.S. Senate Majority Leader Chuck Schumer said on Wednesday that talks with his Republican counterpart Mitch McConnell to avoid a government shutdown were making "good progress." He added, however, that the two leaders must prevent a group of Senate Republicans from causing "total chaos" by delaying action.

The last government shutdown ended after 35 days in January 2019 when several air traffic controllers, who had been working without pay, reportedly called in sick, leading to flight delays and helping to break a political impasse over funding legislation. (Reporting by Jason Lange; Editing by Scott Malone and Nick Zieminski)