The Transportation Security Administration made the announcement in response to the shooting at Los Angeles International Airport two days earlier, when three people, including the gunman, were killed.
Hesham Mohamed Hadayet, an Egyptian immigrant, allegedly began a shooting rampage at a ticket counter of El Al, the Israeli national airline, before shot dead by an airline security guard.
"This incident, even if isolated and regardless of motive, emphasizes that we cannot be complacent about any of the security measures that we put in place at our airports and at the other modes of transportation,'' the agency said in a statement.
"Had this event occurred at another airline counter without armed security guards, the situation unfortunately would have been worse," it said.
It was not clear how many officers will be involved in the new deployment nor whether there would necessarily be a guard at each ticket counter at all times.
The undercover investigators, who have transferred to the new security agency from the Federal Aviation Administration, will look for suspicious individuals and intervene when necessary, the statement said.
The head of an airline passengers' advocacy group welcomed the security agency's actions Saturday.
"We would certainly support more law enforcement officials in all parts of the airport, but we would expect there would be a tremendous amount of coordination with the multiple police forces that are going to be functioning in this environment,'' said David Stempler, president of the Air Travelers Association.
The security agency took over responsibility for screening passengers from the airlines in February, and faces a Nov. 19 congressional deadline for replacing checkpoint screeners with federal employees.
But Thursday's shooting took place in the airport's public areas, before passengers are screened for weapons and bombs. Airport police patrol the facility and airlines are responsible for security at the ticket counters.
The agency said it would put uniformed officers and undercover investigators throughout the airport, both beyond the checkpoints and in the public areas. Initially, the law enforcement officers will be local police working with the security agency.
Separately, an INS spokesman said Hadayet's first petition for permanent residency had been denied.
The Immigration and Naturalization Service rejected Hesham Mohamed Hadayet's request to remain in the country in February 1996, INS spokesman Ron Rogers said in Saturday's Orange County Register. It wasn't clear why.
The agency began deportation procedures, but in 1997, Hadayet was granted permanent residency through his wife, Hala, who received an immigration visa through the Department of States' Diversity Lottery Program, the Register and Los Angeles Times reported.
Hadayet's uncle, Hassan Mostaffa Mahfouz, told The Associated Press in Egypt that Hadayet had only about a year remaining before he qualified for citizenship and that he was happy in the U.S.
"I don't believe what happened," Mahfouz said. "I felt that he could not do that."
Another uncle, Mohamed Abdel-Hafiz told Reuters on Friday that his nephew had no links to Islamic militants.
Police files from Irvine, where Hadayet lived, show officers went to his apartment on a domestic dispute call six years ago, but he was not prosecuted. Nothing else in the files even hints at the violence he unleashed on Thursday, his 41st birthday.
The FBI said Hadayet went to the El Al counter intending to kill people, but his motive remained unclear Saturday.
Israeli officials said they would consider the attack an act of terror unless it was proven otherwise. But on Friday, White House press secretary Ari Fleischer said, "There is no evidence, no indication at this time that this is terrorists."
FBI special agent Richard Garcia said it still wasn't known if Hadayet harbored anti-Israel feelings.
"Besides terrorism and such, we are also looking into the possibility of a hate crime. We're also looking into the possibility of the person being despondent," Garcia said.
Abdul Zahav, a man who said he worked for Hadayet until he was fired two years ago, said Hadayet once told him he hated all Israelis.
"He kept all his anger inside him. So he can't hold it anymore, he can't hold it anymore," Zahav said.
Others painted a far different picture of Hadayet.
"He was never hateful or belligerent," said Dan Danilewicz, whose 17-year-old son was a friend of the Hadayet family. "I can't see him carrying a knife or gun into the airport. Nothing anti-American or anti-Semitic ever came out of their mouths."
Hadayet's wife and sons, Adam, 8, and Omar, 14, had left California for Egypt about a week before the shootings.
Relatives said Hadayet was a Cairo-born accountant who ran a limousine company out of his apartment. Mahfouz said Hadayet studied commerce at Ain Shams University in Cairo and worked as an accountant in a bank before leaving for the U.S. in 1992.
"He is a very, very tender person and close to his family," Mahfouz said.
Irvine police Lt. Dave Freedland said Hadayet had three contacts with the department since 1996 - all of them "unremarkable."
Neighbors said Hadayet was quiet, but once became angry when an upstairs neighbor hung large American and Marine Corps flags from a balcony above his front door after the Sept. 11 attacks.
"He complained about it to the apartment manager. He thought it was being thrown in his face," neighbor Steve Thompson said.
There was no record of such a complaint, said Rich Elbaum, a spokesman for The Irvine Co., which owns the complex where Hadayet lived.
The flags were there the day of the shooting. A bumper sticker on Hadayet's front door that read "Read the Koran" was removed by authorities.
The FBI searched the apartment Thursday night, impounding a Toyota Camry, a computer, books, binders and other material.
Los Angeles officials, meanwhile, sought to assure the public that the city was safe.
"We have no information of any credible threats anywhere in the city of Los Angeles," Mayor James Hahn told reporters outside police headquarters.
In Cairo, Egypt's foreign minister expressed surprise on Saturday at the furor over the attack, saying the motives were still unclear and similar incidents occurred frequently.
Egypt's official Middle East News Agency (MENA) said Egyptian Foreign Minister Ahmed Maher told reporters in Cairo that such incidents occur repeatedly in the U.S. and other countries and said he was surprised by the exaggeration of this event in particular.
Egypt's semi-official al-Ahram daily said on Saturday that local security authorities had no evidence that Hadayet had any links to extremist activities when he lived in Egypt.
The issue is particularly sensitive in Egypt, which fought a bloody battle against Islamic militants at home last decade and whose reputation has suffered from revelations that many of the suspected culprits behind the September 11, 2001 suicide hijack attacks on New York and Washington were Egyptian.
Among the most notorious are Ayman al-Zawhari, a top aide of al Qaeda leader Osama bin Laden, and Mohammed Atta, who flew one of the planes that smashed into the World Trade Center.