About six months ago, Alex Brunet, a recent Northwestern University graduate, moved to Washington and started a new job at the Consumer Financial Protection Bureau as an honors paralegal. It was fitting for Mr. Brunet, 23, who said he had wanted to work in public service for as long as he could remember and help “craft an economy that works better for everyone.”

But about 15 minutes before he was going to head to dinner with his girlfriend on the night before Valentine’s Day, an email landed in his inbox informing him that he would be terminated by the end of the day — making him one of many young workers who have been caught up in the Trump administration’s rapid wave of firings.

“It’s discouraging to all of us,” Mr. Brunet said. “We’ve lost, for now at least, the opportunity to do something that matters.”

Among the federal workers whose careers and lives have been upended in recent weeks are those who represent the next generation of civil servants and are now wrestling with whether they can even consider a future in public service.

The Trump administration’s moves to reduce the size of the bureaucracy have had an outsize impact on these early career workers. Many of them were probationary employees who were in their roles for less than one or two years, and were among the first to be targeted for termination. The administration also ended the Presidential Management Fellows Program, a prestigious two-year training program for recent graduates interested in civil service, and canceled entry-level job offers.

The firings of young people across the government could have a long-term effect on the ability to replenish the bureaucracy with those who have cutting-edge skills and knowledge, experts warn. Donald F. Kettl, a former dean in the School of Public Policy at the University of Maryland, says that young workers bring skills “the government needs” in fields like information technology, medicine and environmental protection.

“What I am very afraid of is that we will lose an entire generation of younger workers who are either highly trained or would have been highly trained and equipped to help the government,” Mr. Kettl said. “The implications are huge.”

The administration’s downsizing could have a lasting impact, deterring young workers from joining the ranks of the federal government for years, Mr. Kettl said.

About 34 percent of federal workers who have been in their roles for less than a year are under the age of 30, according to data from the Office of Personnel Management. The largest single category of federal workers with less than a year of service are 25- to 29-year-olds.

The federal government already has an “underlying problem” recruiting and retaining young workers, said Max Stier, the president of the Partnership for Public Service. Only about 9 percent of the 2.3 million federal workers are under the age of 30.

“They’re going after what may be easiest to get rid of rather than what is actually going to make our government more efficient,” Mr. Stier said.

Trump administration officials and the billionaire Elon Musk, whom the president has tasked with shrinking the federal government, have defended their efforts to cut the work force.

“President Trump returned to Washington with a mandate from the American people to bring about unprecedented change in our federal government to uproot waste, fraud and abuse,” Harrison Fields, a White House spokesman, said in a statement.

Mr. Trump has vowed to make large-scale reductions to the work force, swiftly pushing through drastic changes that have hit some roadblocks in court.

Last week, a federal judge determined that directives sent to agencies by the Office of Personnel Management calling for probationary employees to be terminated were illegal, and the agency has since revised its guidance. Still it is unclear how many workers could be reinstated.

The abrupt firings that have played out across the government so far came as a shock to young employees.

They described being sent curt messages about their terminations that cited claims about their performance they said were unjustified. There was a frantic scramble to download performance reviews and tax documents before they were locked out of systems. Some said they had to notify their direct supervisors themselves that they had just been fired.

On the morning of Feb. 17, Alexander Hymowitz sat down to check his email when he saw a message that arrived in his inbox at 9:45 p.m. the night before. An attached letter said that he had not yet finished his trial period and was being terminated from his position as a presidential management fellow at the Agriculture Department. It also said that the agency determined, based on his performance, that he had not demonstrated that his “further employment at the agency would be in the public interest.”

Mr. Hymowitz, 29, said he was dumbfounded. “My initial thought was, obviously something is wrong,” he said. “How could I get terminated for performance when I’ve never had a performance review?”

Mr. Hymowitz, who had worked on antitrust cases and investigations in the poultry and cattle markets for about six months, said he was not given many further instructions. The next day, he decided to walk into the office and drop off his work equipment. “I just assumed that’s what people do when they get fired,” he said.

Around 8 p.m. on Feb. 11, Nicole Cabañez, an honors attorney at the Consumer Financial Protection Bureau, found out that she had been terminated after she realized she could not log into her work laptop. Ms. Cabañez, 30, worked in the agency’s enforcement division for about four months, investigating companies that violated consumer financial laws.

“I was prepared to help make the world better,” Ms. Cabañez said. “It’s honestly very disappointing that I never got that chance.”

During her first year at Yale Law School, Ms. Cabañez said she originally planned to work at a large law firm, where she would have defended companies and made a lucrative income after graduation. But she said she wanted to work in public service to help people get relief through the legal system.

Ms. Cabañez said she was now applying for jobs with nonprofits, public interest law firms and local governments. But she said she worried that the job market, especially in Washington, would be “flooded with public servants.” She said she could not file for unemployment benefits for three weeks because her agency had not sent her all of the necessary documents until recently.

The impacts have stretched beyond Washington, reaching federal workers across the country, including in Republican-led states.

At 3:55 p.m. on Feb. 13, Ashlyn Naylor, a permanent seasonal technician for the U.S. Forest Service in Chatsworth, Ga., received a call from one of her supervisors who informed her that she would be fired after working there for about nine months. Ms. Naylor said she initially wanted to stay at the agency for the rest of her career.

“It was where I have wanted to be for so long, and it was everything that I expected it to be from Day 1,” Ms. Naylor said.

Ms. Naylor, 24, said she felt a mixture of anger and disbelief. She said her performance evaluations showed she was an “excellent worker,” and she did not understand why she was fired. Although she said she was devastated to lose her job, which primarily involved clearing walking trails in the Chattahoochee-Oconee National Forest, she was not sure if she would return to the agency in the future.

“It would be really hard to trust the federal government if I were to go back,” Ms. Naylor said. She said she was considering enrolling in trade school and possibly becoming a welder since she is still “young enough” to easily change her career.

Although some said their experiences have discouraged them from pursuing jobs with the federal government again, some said they were intent on returning.

Jesus Murillo, 27, was fired on Valentine’s Day after about a year and a half working as a presidential management fellow at the Department of Housing and Urban Development, where he helped manage billions of dollars in economic development grants. After standing in countless food bank lines and working in fields picking walnuts to help his family earn additional income growing up, Mr. Murillo said he wanted to work in public service to aid the lowest income earners.

“I’ve put so much into this because I want to be a public leader to now figure out that my government tells me that my job is useless,” Mr. Murillo said. “I think that was just a smack in the face.”

Still, he said he would work for the federal government again.

“For us, it’s not a partisan thing,” Mr. Murillo said. “We’re there to carry out the mission, which is to be of service to the American public.”