WASHINGTON — Hundreds of thousands of federal employees returned to work on Monday with a presidential promise of a paycheck “very quickly” but no guarantee that they will be working in three weeks, when a temporary stopgap of funding expires.

President Donald Trump and congressional Democrats arrived at a short-term agreement late on Friday, reopening the government after 35 days and the longest government shutdown in history. Lawmakers have until Feb. 15 to reach a compromise on the Republican request for billions of dollars to be allocated for a border wall — a wall Democrats have refused to fund.

Referring to the odds that a deal could be struck over that time, Trump told The Wall Street Journal on Sunday, “I personally think it’s less than 50-50.” Trump said he would use emergency powers to fund the wall if an agreement could not be reached.

In a stark reminder that federal employees were returning to work with the knowledge that they might be forced to go without a paycheck once again next month, one federal agency, the Department of Agriculture, updated its employee information website and said, “We will also leave some of the shutdown-related material up for a period time, should you need to refer back to it.”

Richard Nagle, a lawyer with the Environmental Protection Agency in Chicago, said returning to work after a mandatory furlough required some digging out.

“It’s triage,” he said, eyeing his email inbox. “I’m going to go through the ones that are screaming for attention. I haven’t been on voice mail yet, but I’m sure that’s capped out at 32 messages.”

In the first hour of his day, one question seemed to be echoing through the halls: What did you do?

Colleagues were sharing stories of how they passed the time while they were furloughed. Pretty much everyone confessed to sleeping a little later than usual. Basements were cleaned out, digital photos were organized, hardwood floors were scrubbed until they were gleaming.

Some employees took road trips, visiting extended family in Michigan or driving down to Memphis, eight hours away. Anything to stave off the boredom and anxiety of being home, unpaid, during a Chicago winter.

As employees streamed into the office, managers stood in the lobby, handing out informational papers on things to know: how to apply for back pay, what to do if you forgot your passwords. Some supervisors brought in sweet treats. There were nudges about projects that had been put on hold — and, in some cases, forgotten — and hurried meetings to figure out what could be accomplished before the next potential shutdown.

At a Federal Emergency Management Agency office in Fort Worth, Texas, some employees felt like they were racing against the clock.

“They’re trying to get as much work as they can get done before flood season, tornado season and hurricane season,” said Steve Reaves, a safety officer for FEMA who also leads the union for FEMA employees. “With us, it’s do as much we can before they try to do this again.”

Senior officials on Monday both welcomed their workforces and tried to reassure them about the weeks to come.

“I encourage you all to take time to talk to each other about the past few weeks and be transparent with your supervisors about any hardships,” Brock Long, the FEMA administrator, wrote in an email on Monday morning. “I also want to be clear that there is no higher priority than to guarantee, for those who missed paychecks, that you get paid as quickly as possible.”

But Long acknowledged that reopening the government was not as simple as turning a light-switch.

“While there is important work to be done, I want to make sure that you are set up for success before jumping into your normal assignments,” he wrote. “Please allow time for updates and reboots to computers, addressing expired passwords, syncing mobile devices, managing benefits and organizing your work space. Supervisors have been provided checklists that should be helpful. Again, please also take the time to listen and support each other.”

Ryan Baugh, a Department of Homeland Security statistician and a steward for the American Federation of Government Employees, said the possibility that there could be another shutdown had a damaging effect, raising questions about what could realistically be scheduled — meetings, trainings, projects — given the uncertainty.

“We’ll work hard for three weeks, and then we’ll see what happens,” he said. “You could still use the word ‘hostage.’ We’re still the bargaining chip here.”

The morning commute on Monday in the Washington area was once again bustling after an eerily quiet month of little road traffic during peak travel hours and open seats on trains and buses.

At a Metro station near the Environmental Protection Agency’s headquarters in Washington, a small group of environmental activists with the nonprofit group Mom’s Clean Air Force welcomed EPA employees back to work with cinnamon rolls.

“Welcome back! Cinnamon roll?” Elizabeth Brandt, a field organizer for the group chirped as employees rode up the Metro escalator. Brandt, holding her daughters, Valencia, 5, and Natalia, 3, said that having grown up next to a toxic cleanup site in Tacoma, Washington, it was important to her to make sure the agency’s workers knew their work was valued.

“I don’t often get a chance to thank people who do that work the way I thank our pediatrician and the people who give my kids shots,” she said.

EPA employees said they were relieved to be back to work yet anxious that the reprieve from the partial government shutdown could be short-lived.

“Most of us cannot afford to be without pay for a month,” said Denise Walker, an agency lawyer. “It’s very stressful for people.”

The National Park Service reopened on Sunday, but prospective visitors were encouraged to check with individual parks to make sure they were receiving visitors. Smithsonian museums and the National Zoo were set to reopen Tuesday.

Federal workers who had turned to food banks to feed their families continued to struggle to make ends meet as they returned to work Monday. Some federal employees have been working without pay for weeks. And many federal contractors are not expected to be paid at all for the days the government was closed.

Jamie Rodny, an investigator at the Housing and Urban Development office in Los Angeles, said she was both excited to return to work and scared she would be facing the same situation in three weeks. She was told she would not see a paycheck on Monday, and said her branch chief told her that he had heard they might get paid on Thursday.

Rodny, who works for the Fair Housing and Equal Opportunity division, which oversees the enforcement of federal housing laws, said she arrived at her office to find frantic emails and voice mail messages from people whose cases she was forced to drop when the government closed. Now, as she returns these messages, she expects to hear that some of those complainants were evicted over the past 35 days or are facing debts because of the forced lull in their cases.

“Where do I start,” she asked.

Rodny spoke at the Women’s March in Washington earlier this month, after she was approached by her labor union, the National Federation of Federal Employees, about the financial and emotional pain of workers affected by the shutdown. Her family lives paycheck to paycheck, she said, and during the break in pay, they used their credit cards for as many purchases as possible, which resulted in her credit score dropping. She said they were able to make their mortgage payment because of donations they received through a GoFundMe campaign. She recently started an activist group called “Stop Government Shutdowns Forever.”

The president promised the 800,000 employees who had been furloughed or forced to work that they would be paid “very quickly or as soon as possible,” without providing a specific date. The White House Office of Management and Budget directed agencies to prioritize pay and benefits after reopening.

Some federal agencies worked through the weekend in an effort to get paychecks to their workers as soon as possible. The Department of Agriculture instructed its employees to file their time sheets by noon on Monday and pledged to resume direct deposits into bank accounts by Thursday. On Sunday, the commissioner of the Customs and Border Protection agency, Kevin K. McAleenan, addressed employees on Twitter to say that the agency had already approved a majority of the timecards and pledged to work to make sure everyone is paid soon.

Aware of the looming Feb. 15 deadline, some lawmakers are trying to pass a law that would outlaw future government shutdowns.

“Shutting down the government should be as off limits in budget negotiations as chemical warfare is in real warfare,” said Sen. Lamar Alexander, R-Tenn., said Friday.

This article originally appeared in The New York Times.