(Bastien Inzaurralde/The Washington Post)

President Trump instituted an immediate hiring freeze Monday, signing a presidential memorandum that would affect a large swath of the executive branch but leave wide latitude for exemptions for those working in the military, national security and public safety.

The move — coming on the new president’s first full working day in the White House — represents the opening salvo in what could be the most concerted effort to overhaul the federal workforce in 35 years.

Critiquing the Washington establishment was central to Trump’s campaign, and he placed federal employees at the center of his effort to “clean up the corruption and special interest collusion in Washington, D.C.” His “Contract with the American Voter” listed a hiring freeze as a key element. It was one of several executive actions he issued Monday, including ones to withdraw from the Trans-Pacific Partnership and to block U.S. funds from being distributed to international organizations that perform or discuss abortions.

Trump’s memorandum states that “no vacant positions existing at noon on January 22, 2017, may be filled and no new positions may be created, except in limited circumstances,” although the freeze does not apply to military personnel.

“The head of any executive department or agency may exempt from the hiring freeze any positions that it deems necessary to meet national security or public safety responsibilities,” it reads, adding the head of the Office of Personnel Management can allow for hiring “where those exemptions are otherwise necessary.”

Speaking to reporters Monday, White House press secretary Sean Spicer said there has been “a lack of respect for taxpayer dollars in this town for a long time and I think what the president’s showing through the hiring freeze . . . [is] that we’ve got to respect the American taxpayer.”

“Some people are working two, three jobs just to get by,” he added. “And to see money get wasted in Washington on a job that is duplicative is insulting to the hard work that they do to pay their taxes.”

Trump also instructed the head of OPM to “recommend a long-term plan to reduce the size of the Federal Government’s workforce through attrition” within 90 days, at which point the hiring freeze would expire.

House Government Reform and Oversight Committee Chairman Jason Chaffetz (R-Utah), who is hoping to enact broader civil-service changes that could make it easier to remove workers for misconduct and replace federal pensions with retirement plans often used in the private sector, said in an interview that he was “very supportive of freezing the net numbers of federal employees.”

But he said some agencies, including the U.S. Secret Service and those dealing with cybersecurity operations, had to be able to fill open positions.

“The president is obviously working to fulfill a campaign promise. I concur with the goal,” he said. “In terms of the details on the execution, we would love to work with him.”

The details at this point are a little bit murky.

Vice President Pence, left, and National Trade Council adviser Peter Navarro, right, wait for President Trump to sign three executive orders, Monday in the Oval Office. (Evan Vucci/AP)

Officials at the Pentagon said Monday evening that it wasn’t yet clear whether the freeze would exempt civilian Defense Department personnel, which number roughly 750,000, or only uniformed employees. One Defense official, speaking on condition of anonymity to address internal discussions, said that Pentagon lawyers were examining the directive.

Veterans — who make up 31 percent of the federal workforce — could also be disproportionately affected by the move because they receive a hiring preference when it comes to federal jobs. One unit of the Pentagon, according to an official who asked for anonymity to discuss personnel matters, is in the process of hiring between 20 and 30 veterans and is now looking at whether to put the hires on hold.

Depending on how the exemptions are interpreted, according to New York University public service professor Paul Light, the freeze might affect fewer than 800,000 employees, or more than one-fifth of the overall federal workforce.

“Anyone who’s looking at 1600 Pennsylvania Avenue is looking in the wrong direction,” Light said. “The real action’s going to be on the Hill.”

Still, the move sparked an immediate outcry from federal employee union officials and some public-service advocates.

“There’s real need for change in the federal government, and this is not the kind of change that’s constructive,” Max Stier, president and chief executive of the Partnership for Public Service, said in an interview. “You don’t freeze into place what is already not what you want.”

Richard G. Thissen, president of the National Active and Retired Federal Employees Association, noted that the federal workforce is now roughly 10 percent smaller than it was in 1967.

Thissen said the freeze “would undermine the efficiency of government operations by creating hiring backlogs and inadequate staffing levels, and it is unlikely to save any money.”

The last two major, across-the-board freezes were instituted by Presidents Jimmy Carter and Ronald Reagan, who imposed them after taking office. In 1982, the General Accounting Office (now the Government Accountability Office) issued a report concluding that both freezes ended up costing more money than they saved and were “not an effective means of controlling federal employment.”

Part of that expense stemmed from the hiring of contractors to compensate for staff reductions; Trump’s memorandum makes clear, however: “Contracting outside the Government to circumvent the intent of this memorandum shall not be permitted.”

President George W. Bush imposed a hiring freeze in 2001, but it affected only selected agencies. Under President Obama, some agencies, including the Pentagon, imposed hiring freezes because of budget constraints.

Rachel Greszler, a senior policy analyst with the Heritage Foundation, said it made sense for Trump to impose an initial freeze so he can “evaluate things and see where the waste and inefficiencies are” in the federal government.

“He needs that time so that more federal employees don’t come onto the rolls, because it’s extremely difficult to fire federal employees,” Greszler said.

However, Stier said there are real deficiencies in the federal government already, and a freeze will just exacerbate them. The government spends nearly 80 percent of its $90 billion IT budget on operations and maintenance, and there are nearly three times as many employees over age 60 as under age 30.

“That’s not the workforce you want to freeze; you want to refresh it,” he said.

The move will likely translate into a grayer federal workforce, where the average age is around 50. Rep. Don Beyer, a Democrat who represents federal workers in his Virginia district, noted that a third of career employees are eligible for end-of-career benefits in September 2017. Without replacements, the average age “gets a year older every year.”

And Rep. Gerald E. Connolly (D-Va.), who also represents federal employees, said they are “used as a political punching bag,” warning that the instructions will affect people throughout the country. Eighty-five percent of the federal workforce, he noted, “lives outside the Beltway.”

“So for lawmakers who think this only affects people inside the Beltway, think again,” he said in an interview. “This will affect your veterans’ services, your Social Security services, your national parks, your forests.”

Rep. Barbara Comstock (R-Va.) also does not support what she called in a statement “this type of across-the-board freeze.”

Missy Ryan and Lisa Rein contributed to this report.