The National Transportation Safety Board, in reports released Friday, said critical failings by Metro contributed to several rail accidents, including one in 2010 that killed two Metro technicians.

The NTSB said “inadequate safeguards” to warn when crews were working on the tracks contributed to the deaths of the workers, who were struck and killed by track equipment in Rockville.

In another incident, a February 2010 train derailment, the board found that the train operator’s failure to follow procedures led to the mishap at the Farragut North station.

In the third incident reviewed, the board found that operator fatigue led to one train striking another in the West Falls Church rail yard in November 2009.

NTSB Chairman Deborah A.P. Hersman said in a statement that “any transit agency must ensure the safety of its employees as well as its passengers.”

She said “an effective safety management system” is “the central part of an organization’s operating plan and it must be understood and embraced by all employees, at all times.”

The reports come three days after a longtime Metro mechanic was critically injured when he was struck by a train in a rail yard near the Shady Grove stop.

The mechanic walked in front of a four-car train in the carwash area of the yard, a witness told Metro safety investigators, according to the agency. The victim was trapped under the first car, and rescue workers had to lift the train and cut away pieces of the track to extricate him, a process that took nearly an hour. Union leaders said they were told that the man lost part of his leg. The NTSB is aware of the accident, and Metro is investigating the cause.

The NTSB’s findings in the earlier accidents also come as watchdogs are pushing for Congress to implement federal safety standards for Metro and other subway systems. There are no uniform safety standards for running subway systems like those for operating airplanes or driving trucks long distances.

Richard Sarles, Metro’s general manager, said in a statement Friday that “we welcome the NTSB’s thorough reviews of these incidents, which serve as important reminders of our number one priority: ‘safety.’ ”

NTSB’s report on the Jan. 26, 2010, incident near the Rockville station, in which equipment moving on the tracks killed two technicians, said several factors were at play.

The NTSB cited Metro for having “inadequate procedures” to protect workers on tracks, and it said there is “inadequate federal agency oversight” of such policies. The safety board also said Metro’s operations control center had “inadequate communication” among the various groups working on the tracks.

One of the technicians had given a cellphone number to an operator at Metro’s command center, and the operator had agreed to give it to “anyone entering the work area so they could communicate directly.” But the operator never gave it to the track-equipment crew.

The NTSB found that had the operator given the crew members the number and “instructions to coordinate their work, the accident could have been prevented.”

The NTSB said Metro also lacked proper alarms for vehicles working on tracks — a problem the agency says it has corrected by retrofitting its track equipment with audible signals and more lighting.

The transit agency said it also has trained or recertified more than 8,500 of its employees in its safety training program to warn crews of the dangers of working on the tracks.

In the Farragut North incident, on Feb. 12, 2010, a Red Line train with 345 passengers derailed because the train operator passed a red signal, according to the NTSB. Three passengers were treated for minor injuries. The accident caused about $174,000 in damage.

According to the NTSB report, the radio transmissions between the train operator and the command center were “weak and garbled at times” after the operator saw a red signal and went onto a side track. The operator moved her train forward when she had not received orders from the center.

The report also faulted a supervisor for not properly overseeing the operator.

On Nov. 28, 2009, a train hit the back of a standing train in the West Falls Church rail yard, causing minor injuries to three Metro workers. The accident caused about $9 million in damage.

One of the problems, the NTSB found, was that the train operator had “received a limited amount of sleep the night before the accident” and had been awake for more than 17 hours, causing him to be fatigued at the time of the incident.