More than 2.5 million Americans will head to airports this weekend dreading their encounters with a common adversary: people like Shekina Givens and the other employees of the troubled federal agency she works for, the Transportation Security Administration.

The TSA’s uniformed screeners have become convenient scapegoats for the long lines, missed flights and general chaos that have frustrated airline travelers all month. And even if airports are relatively calm this weekend — and there is early evidence that may be the case — the agency itself has become a symbol of government inefficiency.

“To say customers are agitated is putting it mildly, and the public outcry has resonated,” Kerry Philipovitch, a senior vice president of American Airlines, told members of a congressional subcommittee Thursday.

But Givens, a TSA screener at Hartsfield-Jackson International Airport in Atlanta, says the anger is misdirected. She and her colleagues argue that the agency has been denied the resources it needs to contend with the expanding horde of passengers.

“We are doing more with less for years at this point,” she said, “and the long lines are proof of what’s been going on.”

The TSA’s workforce and budgets have in fact been shrinking. The agency’s rolls have shrunk to about 44,900 screeners today from 47,000 in 2013, even as passenger travel has increased 15 percent. But it is also true that it has been plagued by mismanagement and other problems of its own making. An unloved stepchild of the Department of Homeland Security, the TSA has suffered through constant turnover in leadership, repeated misconduct by senior managers, low staff morale and high rates of attrition among screeners.

“My opinion is that a structural change is needed,” said Thomas L. Bosco, director of aviation for the Port Authority of New York and New Jersey “The current model that TSA has is not sustainable.”

The Port Authority and other airport agencies are considering hiring private screeners instead of using the TSA. But the TSA would still have oversight of the private screeners.

It’s hard to find travelers who would disagree with Bosco.

“We know when people are coming and how many,” K.P. Reddy, a venture capitalist, said as he waited for a flight to Scotland at Hartsfield on Thursday. “It’s not like road traffic. It’s simple math to have enough people.”

Michael Boyd, president of Boyd Group International, an aviation consulting firm, has a harsher assessment. “Their job is to have enough people to make this work. They don’t have enough people. Therefore, they failed.”

Peter V. Neffenger, the retired Coast Guard admiral who was appointed administrator of the agency last summer, admitted as much in an interview Thursday. He described the agency he took over as “an organization in crisis,” both internally and in terms of public confidence in it.

“We really needed to step back and build the institution in a more deliberate way,” Neffenger said.

Created in the aftermath of the Sept. 11 terrorist attacks, the TSA has long struggled to balance the efficient screening of passengers and their baggage with the paramount goal of ensuring safety.

From the beginning there were problems. The agency’s first administrator, John W. Magaw, was dismissed after just six months on the job, after criticism that he did not work well with lawmakers or airline or airport officials. He also was criticized for long security lines resulting from the TSA’s screening methods.

Through a series of leadership changes, travelers continued to complain about invasive scanning machines and unfriendly screeners. John S. Pistole, a former deputy director of the FBI, arrived at the TSA in 2010 and tried to emphasize the agency’s counterterrorism mission while seeking ways to speed up the screening process.

Pre-Check, an expedited screening system conceived by Pistole, was supposed to alleviate long waits by clearing many passengers to keep their shoes and jackets on at checkpoints, and leave laptops and small containers of liquids in their carry-on bags. With those travelers ushered through exclusive Pre-Check lanes, screeners could devote more scrutiny to people the agency thought posed greater risk.

But agency officials relied on overly optimistic projections of Pre-Check’s appeal, estimating that millions of people would pay the $85 fee to enroll in it.

During a hearing, Pistole, who stepped down as head of the TSA last year, told lawmakers that programs like it would not only save the agency money but “result in a smaller, more capable workforce focused on our counterterrorism mission.”

John Roth, the inspector general for the Department of Homeland Security, said the subsequent cuts were a major cause of the slowdown passengers are experiencing.

“The reasons for the long lines we are seeing are not mysterious,” Roth said. “TSA reduced its workforce from previous levels because it believed that it would gain efficiencies from implementing what it called ‘intelligence-driven risk-based procedures.’”

With the lanes set aside for Pre-Check underused, the agency started selecting passengers who had not been preapproved to bypass the standard lines during periods of high traffic to go through the less rigorous screening. But the agency’s own classified review of the program, which came to light in a recent congressional hearing, revealed significant security gaps.

An assistant security director disclosed that Sara Jane Olson, who was convicted in a plot by members of a 1970s radical group to kill Los Angeles police officers, was allowed to use an expedited inspection lane even after having been recognized.

Pistole defended his decision to reduce the TSA workforce, saying the risk-based screening approach had worked. The problem, he said, was that the agency changed its detection methods.

“There are only so many options you can use to improve detection and one is to be more thorough, which takes more time,” he said. “Thoroughness and increased passenger traffic created a perfect storm for what you see now.”

The agency also faced a number of whistle-blower lawsuits claiming that senior managers retaliated against employees who reported security lapses and awarded bonuses to supervisors who ignored their warnings. Other stories emerged that raised questions about the agency’s management.

One senior official, Kelly Hoggan, who was assistant administrator for the Office of Security Operations, received $90,000 in bonuses over a 13-month period, even though a leaked report from the Department of Homeland Security showed that auditors were able to get fake weapons and explosives past security screeners 95 percent of the time in 70 covert tests.

Neffenger drew the ire of many employees during a congressional hearing this month when he said he would not discipline or remove Hoggan, adding that he had no evidence of any wrongdoing. But he has since replaced Hoggan, who is on paid leave, and put limits on the amount of bonuses that employees can receive.

Not all the TSA’s troubles can be blamed on missteps by the agency. The dysfunction has been compounded by an earlier 2013 bipartisan budget deal negotiated between Sen. Patty Murray, D-Wash., and Rep. Paul D. Ryan, the current House speaker, to avoid a government shutdown.

The deal set the security fee assessed on each segment of a plane trip to $5.60, but called for 60 cents of that fee to be diverted from the TSA to pay down the national debt. This year, $1.25 billion in fees is going into the Treasury instead of paying for screeners and new equipment.

J. David Cox Sr., president of the union that represents the screeners, the American Federation of Government Employees, said that if the TSA kept all of the fees, it could restore the 6,000 workers it had lost in the last five years, and pay them better. All screeners start out as part-timers and some earn less than $15 an hour, Cox said.

The dwindling of their ranks, while the number of passengers keeps rising, has been deeply frustrating, Cox said. “They sort of feel like they’re at the ocean with a dipper every day,” he said.

Part of that is because of low morale and high attrition. To address the problem, Congress has allowed Neffenger to retain 1,600 jobs that the TSA had planned to cut this year. Jeh Johnson, the Homeland Security secretary, has also asked Congress to allow the agency to redirect an additional $28 million to pay for shifting 2,784 part-time screeners to full-time work at the 20 busiest airports.

Hoping to avert a disastrous start to the summer, Neffenger said, he has sent a “surge” of additional officers and deployed most of the agency’s explosive-detecting dogs to those critical hubs.

Airlines are pitching in, too. In Atlanta, Delta Air Lines rolled out new equipment this week for sorting travelers’ carry-ons faster. At New York’s Kennedy International Airport, a group of airlines pitched in $250,000 to hire workers, starting Friday, to help TSA security officers explain the rules and help out at the security checkpoints.

As the Memorial Day weekend began, those measures appeared to be making a difference. Travelers who got an early start Thursday said they were pleasantly surprised by how short the lines at checkpoints were and quickly they moved.

At Chicago’s O’Hare International, Erin Antonyzyn, 38, a teacher who was flying to Cincinnati to see her family, said she arrived at the airport two hours early but made it through security in 10 minutes. And she had words for the TSA that it rarely hears.

“I think they obviously made some smart decisions,” she said.

© 2016 The New York Times Company