President Obama speaks at the Centers for Disease Control and Prevention in Atlanta on Sept. 16. It was during that visit that an armed security contractor was allowed to ride an elevator with Obama, in violation of Secret Service protocols. (Pablo Martinez Monsivais/AP)

Correction: This story has been updated to correct descriptions of the armed man who rode an elevator Sept. 16 in Atlanta with President Obama. While agents found he had prior arrests, according to people with knowledge of the incident, they found the man is not a convicted felon, as an earlier version reported. The Post reported new details provided about the man’s record here.

A security contractor with a gun and an arrest record was allowed on an elevator with President Obama during a Sept. 16 trip to Atlanta, violating Secret Service protocols, according to three people familiar with the incident.

Obama was not told about the lapse in his security, these people said. The Secret Service director, Julia Pierson, asked a top agency manager to look into the matter but did not refer it to an investigative unit that was created to review violations of protocol and standards, according to two people familiar with the handling of the case who spoke on the condition of anonymity.

The incident, which took place when Obama visited the Centers for Disease Control and Prevention to discuss the U.S. response to the Ebola crisis, rattled Secret Service agents assigned to the president’s protective detail.

The private contractor first aroused the agents’ concerns when he acted oddly and did not comply with their orders to stop using a cellphone camera to record the president in the elevator, according to the people familiar with the incident.

When the elevator doors opened, Obama left with most of his Secret Service detail. Some agents stayed behind to question the man and then used a national database check that found some prior arrests in his historyturned.

When a supervisor from the firm providing security at the CDC approached and discovered the agents’ concerns, the contractor was fired on the spot. Then the contractor agreed to turn over his gun — surprising agents, who had not realized that he was armed during his encounter with Obama.

Under Secret Service protocols, people with weapons, arrests or convictions for assault and related offenses or any history of mental illness are typically barred from having any access to the president. But it appears that this man, possessing a gun, came within inches of the president after undergoing no such screening.

Rep. Jason Chaffetz (R-Utah), who heads a House subcommittee that oversees the Secret Service, first heard of the breakdown from a whistleblower. The Washington Post confirmed details of the event with other people familiar with the agency’s review.

“Words aren’t strong enough for the outrage I feel for the safety of the president and his family,” Chaffetz said.

Chaffetz added: “His life was in danger. This country would be a different world today if he had pulled out his gun.”

A Secret Service official, speaking on behalf of the agency, said an investigation of the incident is ongoing. The official spoke on the condition of anonymity, citing the pending review.

A White House spokesman declined to comment on the incident or say when, or if, the president had been informed of it.

In response to a question at a combative House hearing Tuesday, Pierson said she briefs the president “100 percent of the time” when his personal security has been breached. However, she said that had happened only one time this year: when Omar Gonzalez jumped over the White House fence Sept. 19 and was able to burst into the mansion.

The revelation of the lapse in Atlanta is the latest in a string of embarrassments for the Secret Service. Some elements of the incident were first reported Tuesday afternoon on the Washington Examiner’s Web site.

Pierson drew criticism Tuesday from lawmakers in both parties during the hearing on her agency’s security lapses. The session focused on the Secret Service’s fumbled responses to the recent White House fence jumper and a 2011 shooting attack on the residence.

The fence breach came three days after Obama’s trip to Atlanta.

The elevator incident exposed a breakdown in Secret Service protocols designed to keep the president safe from strangers when he travels to events outside the White House.

Under a security measure called the Arm’s Reach Program, Secret Service advance staffers run potential event staff members, contractors, hotel employees, invited guests and volunteers through several databases, including a national criminal information registry, and records kept by the CIA, the National Security Agency and the Defense Department, among others. Anyone who is found to have a criminal history, mental illness or other indications of risk is barred from entry.

Local police and federal officers are not checked in the same way under the Arm’s Reach Program, with the Secret Service presuming that they meet the safety standards because of their employment in law enforcement. But private security contractors would typically be checked, said two former agents who worked on advance planning for presidential trips.

For nearly every trip the president takes, at least one person is barred from attending or participating in an event because of problems discovered in his or her background, the two former agents said. Most recently, a local political campaign volunteer who was offering to help drive staffers to and from events during a visit had faced an assault charge in the past.

As part of the Secret Service’s review of the elevator incident, Pierson directed a supervising agent on the president’s protective detail to stay in Atlanta to examine the breakdown.

That decision aroused suspicion on Capitol Hill. Chaffetz said he believes that Pierson was trying to keep another security gaffe quiet at a time when her agency and her leadership are under fire.

Former and current agents say Secret Service leaders prefer this kind of informal internal review for assessing potentially embarrassing mistakes. They say such reviews rarely lead to broad reforms or consequences.

These agents also say it is problematic for a presidential protective detail supervisor to review how his team performed.

In an incident The Post revealed in 2013, a top manager of the president’s protective detail had met a woman while drinking at a bar at the Hay-Adams hotel and had left a bullet from his service weapon in her room after spending the evening with her there. One of his superiors reviewed the incident and at first recommended that he receive a few days of counseling. The Post report about the episode led to the agency launching a fuller investigation.

Julie Tate contributed to this report.