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(CNN) — The U.S. Department of Homeland Security will immediately increase the use of overtime and work to quickly bring in more screening officers to help alleviate long lines at airport security checkpoints, Homeland Security Secretary Jeh Johnson said Friday.

But Johnson warned that longer wait times are inevitable during the busy summer travel season.

"We encourage people to have the appropriate expectations when they arrive at airports," Johnson said at a news conference at Reagan National Airport outside Washington. "Contemplate increased wait times as you travel."

The Transportation Security Administration also will move to accelerate the hiring of 768 new security officers it had planned to bring on during 2016, Johnson said. The agency hopes to have those officers in place this summer, possibly as early as mid-June, he said.

The TSA will take other steps, including deploying more dogs to assist in screening and seeking help from airlines with "nonsecurity" work such as moving bins, Johnson said.

But the government cannot take shortcuts that could endanger security. "We want to keep passengers moving, but we want to keep passengers safe," Johnson said.

'Insane' lines

The TSA confronted a barrage of images this week from travelers documenting the hours-long checkpoint lines at airports across the United States.

American Airlines held five flights for delayed passengers at the Dallas-Fort Worth International Airport on Friday, spokesman Ross Feinstein said. About 20% of those passengers were headed to Las Vegas and 27 passengers were going to Orlando, Florida.

"It is an ongoing problem," said Feinstein.

"Never seen a security line this long at LaGuardia - what's going on @united and @NY_NJairports ?? #hatethewait," tweeted @LisaAkey on Friday morning.

Kym Jones waited in line for two hours Friday at Atlanta's Hartsfield-Jackson International Airport.

"This line starts at the sliding departure doors by check in, zig zags through the baggage claim belts, though the lobby and finally to TSA," Jones tweeted.

She said she only made her flight because a TSA officer told her to go to the international terminal, which had a much shorter security line.

The Atlanta airport closed one security checkpoint last week to install new equipment for an expedited screening process that's scheduled to go into testing later this month.

By midmorning Friday, Atlanta's snarled, serpentine security lines had dissipated, and passengers were moving through checkpoints, CNN staffers there reported.

#iHateTheWait

Airlines for America, an airline industry group, is asking fliers to take photos of security lines and post them to social media with the hashtag: #iHateTheWait

Several of the busiest airports have threatened to replace the TSA with private passenger screening companies.

The Port Authority of New York and New Jersey, which operates Newark, John F. Kennedy and LaGuardia airports, was the latest agency to demand that the TSA add more staff to reduce wait times in security lines.

From mid-March to mid-April, there were hundreds of times that passengers waited more than 20 minutes -- and sometimes more than 55 minutes, a Port Authority letter said.

In February, Atlanta's airport -- the busiest passenger airport in the world -- sent a letter to the TSA complaining about "inadequate" staffing and warning about increasing passenger traffic this summer.

Adding to the TSA's woes: Thousands of checked bags missed their flights Thursday at Sky Harbor Airport in Phoenix after computer server issues kept the TSA from using machines to screen baggage.

TSA looking for more money

TSA Administrator Peter Neffenger blamed the long lines on a loss of thousands of employees in 2014 that the agency has yet to replace.

"When I came into this organization last year, I found an organization with 5,800 fewer screeners, and it had fewer front-line officers than it had four years previously," said Neffenger, testifying Thursday before the House Oversight Committee

"And that was in the face of significantly higher traffic volume."

For fiscal year 2016, the TSA's authorized staffing level is 42,525 and passenger volume is projected to be 740 million, according to the TSA. There's been a 15 percent increase in passenger volume and a 10 percent drop in staffing since fiscal year 2013.

The union representing TSA officers called on Congress to pass emergency legislation funding the hiring of an additional 6,000 full-time screeners.

"Congress has starved TSA of the resources it needs to meet growing demands at our nation's airports," American Federation of Government Employees National President J. David Cox Sr. wrote in a letter sent Thursday to House and Senate leaders.

Congress did give the agency some relief earlier this week.

About $8 million will go toward the hiring of 768 officers this month.

Atlanta airport's experiment

Atlanta's airport, which handled a record 100 million passengers last year, may provide a solution.

The airport temporarily closed one of three domestic TSA checkpoints May 4 for installation and calibration of two experimental screening lines that are expected to open May 24.

The shutdown forced thousands of daily domestic travelers to other checkpoints. That -- along with seasonal traffic -- is making Atlanta's TSA lines worse than usual.

The experimental screening areas -- so-called Innovation Lines -- are now being developed only at Atlanta's airport, the agency said, with the aim of screening more passengers in less time. If successful, they could be replicated at other U.S. airports.

In the meantime, travelers enrolled in TSA's PreCheck program are moving through lines at a faster pace.

PreCheck member Celeste Cooper took five minutes to clear security Friday morning at New Orleans' Louis Armstrong International Airport.

"There was a very long line," Cooper said after landing in Atlanta. "But the TSA PreCheck went very smoothly, very quickly."