The air traffic supervisor who dozed off in the Reagan National Airport control tower early Wednesday, forcing passenger plane pilots to land on their own, was drug-tested by federal authorities before being suspended from his job, federal officials said.

The Federal Aviation Administration declined to confirm the testing or to comment on the results.

FAA Administrator Randy Babbitt suspended the veteran controller supervisor on Thursday, saying he was “personally outraged” after two planes carrying a total of 165 people landed without help from the control tower.

The National Transportation Safety Board on Thursday initiated a formal investigation into the incident, and the House Transportation Committee planned to conduct a formal review.

“This incident and other recent performance failures, including near-miss incidents, are matters of serious concern,” said Rep. John L. Mica (R-Fla.), the committee’s chairman. “I am asking . . . the committee’s investigative staff to conduct a thorough review of this and other recent mishaps.”

Rep. Nick J. Rahall II (W.Va.), the committee’s ranking Democrat, endorsed the probe, adding that “if wrongdoing is discovered, appropriate action must be taken immediately.”

The NTSB said the controller supervisor told investigators in an interview Thursday that he was working his fourth consecutive overnight shift and had fallen asleep. A controller since 1990, he was called in to be drug-tested at National about 12 hours after the incident, federal officials said.

“They rarely drug-test unless it’s an accident,” said an FAA official familiar with the incident, who spoke on the condition of anonymity because he is not authorized to speak for the agency.

Transportation Secretary Ray LaHood has ordered a second air traffic controller to be on duty overnight at National and instructed the FAA to examine staffing levels at airports across the country. Most major airports that operate 24 hours a day have two controllers in the tower for the midnight-to-6 a.m. shift., according to the National Air Traffic Controllers Association.

Dulles International Airport has two, as do the major airports in New York, Newark and Boston. Chicago’s O’Hare International has three. The number on duty at Baltimore-Washington International Marshall Airport was not immediately available.

The issue of tower staffing arose five years ago, when Comair Flight 191 turned onto the wrong runway at a Lexington, Ky., airport. The runway was too short, and the plane crashed on takeoff, killing 47 passengers and two of the three crew members.

Investigators determined that there was only one controller in the tower, a violation of that airport’s policy.

Until LaHood ordered otherwise late Wednesday, the National tower had been staffed by one air traffic controller from midnight to 6 a.m. As planes approached to land early Wednesday, the on-duty controller did not respond to pilots’ requests for landing assistance or to phone calls from controllers elsewhere in the region, who also used a “shout line,” which pipes into a loudspeaker in the tower, internal records show.

The planes — an American Airlines Boeing 737 flying from Miami with 97 people on board, and a United Airlines Airbus A320 flying from Chicago with 68 people on board — landed safely within minutes of each other, just after midnight.

Because the controller was not available, the planes’ pilots took matters into their own hands, broadcasting their progress as they approached and landed. They also were communicating with controllers at a separate facility in the region that does not handle landings.

When the tower supervisor first came back on the radio Wednesday morning, he identified the problem that caused the silence, in a conversation with a pilot, as a “stuck mike.”

In the unlikely scenario of a radio failure, the tower is equipped with a light system visible to arriving pilots. If it was clear to land, the tower controller would flash a green light. If another plane or an airport vehicle was on the runway, the controller would give a red signal.

The lights were not put to use Wednesday morning, according to a review of radio transmissions and another FAA source familiar with the incident.

“Even if he got flustered and forgot about the lights as the first plane approached, you would think he’d come to his senses and use it after one plane landed in front of him and he saw another coming in,” said the source, who spoke on the condition of anonymity because he also is not authorized to speak for the agency.

The incident is the second time that the tower has gone silent. On Dec. 24, 2007, the supervisor controller on duty during the overnight shift left his swipe-card pass key behind when he stepped outside the tower’s secure door and was unable to get back in.

In that case, according to a transcript of radio transmissions, the tower was silent for almost an hour as four aircraft sought guidance — an AirTran Airways flight, an American Airlines flight, a Fairfax County police helicopter and a U.S. Coast Guard helicopter.

All four aircraft landed safely, once again with help from controllers at the Potomac Terminal Radar (TRACON) facility, who stepped in Wednesday morning when the National tower was silent. Those controllers direct planes to and from cruising altitudes but hand off responsibility to the tower for takeoffs and landings.

Babbitt saluted the TRACON backup Thursday for stepping in to help the pilots land.

“Fortunately, at no point was either plane out of radar contact, and our backup system kicked in to ensure the safe landing of both airplanes,” Babbitt said.

The NTSB investigator is scheduled to interview the ­TRACON controllers Friday.