The head of the Transportation Security Administration denied Wednesday that top agency officials intended to tip off airport security screeners that they were being covertly tested last year.

An April 28, 2006 e-mail sent by a TSA employee to airport security officials across the country described an undercover Transportation Department test of screening checkpoints. But agency Administrator Kip Hawley said the message was sent not as a tip-off, but out of concern that al-Qaida or other terrorists might be posing as transportation officials.

The incident, now under investigation by the Department of Homeland Security's watchdog, was the topic of a heated congressional hearing on Wednesday.

At issue is whether aviation security screeners have been told ahead of time that there would be covert testing at their airports. Doing so would defeat the point of the covert tests. TSA, which is part of the Homeland Security Department, conducts thousands of these tests each year in an effort to spot weaknesses in the screening system.

Former Homeland Security Inspector General Clark Kent Ervin said the April incident is part of a pattern of tip-offs. Past investigations found cheating by screeners at Jackson-Evers International Airport in Mississippi and at San Francisco International Airport, the IGs report found.

Hawley said he is not aware of any other incidents. In addition to the TSA tests, the Government Accountability Office and the Homeland Security inspector general also conduct their own checkpoint tests.

"Knowledgeably tipping off covert testing is wrong," Hawley told lawmakers, but he added that didn't happen on April 28.

"There was no intent to tip off," he said. "There was no cheating."

The chairman of the House Homeland Security Committee said Wednesday was the first time Hawley admitted the e-mail was sent. "I think some of this is clearly a breach of what I would consider TSA policy," said Rep. Bennie Thompson, D-Miss. "When errors like this occur, I think Kip Hawley has to be forthright and take appropriate actions."

The April 28 e-mail was sent under the name of the agency's assistant administrator of security operations, Mike Restovich, and warned that "several airport authorities and airport police departments have recently received informal notice" of security testing being carried out by the Department of Transportation and the Federal Aviation Administration.

The e-mail relayed an alert that described a couple who were testing security. The woman is white but has "an oriental woman's picture" on her identification card, it stated. "They will print a boarding pass from a flight, change the date, get through security (if not noticed) and try to board a flight and place a bag in the overhead."

Neither the Transportation Department nor the Federal Aviation Administration — which were referenced in the e-mail — conduct undercover tests at TSA checkpoints, Hawley said.

Hawley told lawmakers Restovich did not send the e-mail, but it was sent out under his name. The official who sent the e-mail found the reference to these two agencies suspicious and decided to share it with federal security directors at airports across the country, he said.

Hawley would not provide the name of the TSA employee who sent the e-mail but said that employee received a tip from someone else and decided to cut and paste it into an e-mail.

The e-mail was recalled 13 minutes after it was sent out, Hawley told lawmakers. But when the agency provided to the congressional committee a list of e-mails sent on that date, the recall was not included. Hawley said he couldn't answer further questions about it because the agency inspector general now has custody of all the computer hard drives and backup records.