“This is not just an inside-the-Beltway political jousting. Failure to fund DHS fully has real impacts on public safety,’’ DHS Secretary Jeh Johnson said Thursday at a news conference. (Win McNamee/Getty Images)

If the Department of Homeland Security shuts down Friday night, Americans likely won’t see much of an immediate impact, as DHS personnel will still protect the president, patrol the borders and screen passengers at airports.

But at DHS facilities in Washington, employees who manage large federal contracts, monitor cyber threats and give grants to local police departments will be sent home, according to current and former DHS officials. If there is a terrorist attack or natural disaster, the effect will be magnified and the government’s response slowed, they said.

And although about 85 percent of DHS’s roughly 240,000-strong workforce will remain on the job, most employees will work without their biweekly paychecks.

With Congress at an impasse Thursday over how to avoid a partial shutdown, DHS Secretary Jeh Johnson continued his media campaign and appealed again for funding. “This is not just an inside-the-Beltway political jousting. Failure to fund DHS fully has real impacts on public safety,’’ he said at a news conference.

Congressional Democrats have gone further than Johnson’s generally measured remarks, warning that a shutdown would cause a national security crisis at a time of continuing terrorist threats. Some Republicans have maintained there will be little impact, pointing out that a large majority of DHS employees worked during the 2013 government-wide shutdown and would do so again during a new stoppage.

“This is a debate over funding a part of government so essential that if funding is not there, almost all of the employees show up anyway. They’re considered essential,’’ Sen. Roy Blunt (R-Mo.) said recently on the Senate floor.

While the most critical DHS functions — such as border and airport security and immigration enforcement — would continue, a review of the 2013 shutdown showed that some effects will be felt acutely in areas where the department already faces problems.

Hiring would cease in an agency that has wrestled for years with high employee turnover. Morale would be devastated, DHS officials said, just as they are taking steps — such as improved training and more internal recognition of employees — to address deep dissatisfaction among workers.

“This is crippling to morale,’’ said Matt Chandler, a former DHS deputy chief of staff who was at the agency during the 17-day shutdown in 2013. “When you inject uncertainty for families who may be relying on this income to pay their bills, there is a real impact felt by those individuals and their families.’’

DHS has also been riddled with management problems, largely stemming from the challenge of welding 22 separate government agencies into one when it began operations in 2003. Just as the department won praise for its efforts to improve management in a recent Government Accountability Office report, many top managers at headquarters would be furloughed.

“While the rest of the workforce would continue to perform vital functions,’’ said Marsha Catron, a DHS spokeswoman, “the bulk of DHS management and headquarters administrative support activities would cease, including much of the homeland security infrastructure that was built following the 9/11 terrorist attacks.’’

The 2013 shutdown provides a template for how DHS would be affected this time. A 2013 Congressional Research Service report found that an estimated 31,295 DHS employees were furloughed, but about 85 percent of the department’s workforce remained on the job.

The report said that “the total number of employees furloughed was relatively small compared with the overall size of the department,’’ but it pointed to a number of significant effects.

DHS procurement “activities were disrupted to some extent,’’ the report said, noting that DHS is the sixth-largest federal agency for procurement spending.

Other effects included the suspension of E-Verify, a program businesses use to determine the work eligibility of new employees, and a shutdown of the department’s civil rights and civil liberties complaint lines.

In the cyber arena — where DHS plays a key role in combatting attacks aimed at civilian federal networks and communicating with critical industries — there would be further impacts from a shutdown, DHS officials said.

For example, they said, the National Cybersecurity and Communications Integration Center — the department’s 24-hour-a-day cyber response center — would have to cut staffing by nearly 60 percent. “Reduced staff would impede and slow down the NCCIC’s day-to-day capability to provide relevant, timely and accurate cyber threat information to federal civilian networks and the private sector for network defense,’’ Catron said.

The Federal Emergency Management Agency would suffer potentially drastic effects, with numerous workers sent home.

“I’ve heard some claim that DHS operations wouldn’t suffer too much during a shutdown. I can tell you this is categorically false,’’ FEMA Administrator Craig Fugate wrote in a recent blog post.

Chris Cummiskey, a former acting undersecretary for management at DHS, said the 2013 shutdown highlighted other effects that may seem smaller but are often difficult to manage. For example, he said, the department spent time writing letters to mortgage companies on behalf of employees who were not getting paid. Resentment built, he said, among those working because they weren’t getting paid and among those deemed non-exempt and sent home.

In the event of a new shutdown, Cummiskey said, “in terms of the public-facing pieces of the department, you’re still going to see a guy in a blue shirt at a checkpoint. You’re still going to see a guy in a green shirt at the border. You’re still going to see a guy in a navy blue shirt at customs.

“But it will be a ghost town at DHS headquarters,’’ he said. “That’s not what you want in an organization with this type of mission.’’