Metro's in-house investigation of the subway derailment that killed three passengers last month has concluded that a wide range of Metro employes committed a series of dangerous errors before and after the accident, errors that it suggested were due to the transit system's "inadequate" training program.

While the report released yesterday reaffirmed earlier findings that put heavy blame on the train's operator and a supervisor who was on the scene, it emphasized that other personnel in Metro's central control room violated standard procedures at a number of points.

Despite calls to the room to keep power off at the accident site, for example, controllers allowed the potentially deadly 750-volt "third rail" to turn back on automatically 37 minutes after the crash, the investigation found. Passengers apparently were still being evacuated from the train at the time.

"Our initial impression is that training is erratic, inadequate and lacks direction and Metro cannot escape responsibility," said the report, adding that, " . . . budgetary restrictions have hindered the programs of retraining, testing and recertification."

Metro General Manager Richard Page conceded that the report constituted a serious indictment of the transit system as a whole, but cautioned that firm conclusions have not been reached. "We do not have any intention of . . . finding a scapegoat," Page said, promising a full search for the accident's cause.

Despite the derailment--Metrorail's first fatal accident since the system opened in 1976--the trains remain an extremely safe way to travel, he said.

The Orange Line train, headed to New Carrollton with a full load of 1,200 people, derailed while backing up from an improperly closed rail switch between the Smithsonian and Federal Triangle stations about 4:30 p.m. on Jan. 13.

After inadvertently entering track normally used to switch trains between the tunnel's two parallel tracks, the lead car's front wheels caught on one main track while its rear ones remained on the other. When the supervisor began backing the train up, the car was dragged diagonally for about 150 feet before being crushed against a concrete pillar between the tracks. Three people died and 25 were injured.

The derailment occurred during a heavy snowstorm, 30 minutes after an Air Florida jetliner crashed into the Potomac River, killing 78 people.

Metro's initial analysis laid heavy blame on the six-car train's operator and a supervisor who had been sent to the defective switch to work it manually. Yesterday, Metro iden-tified the two, for the first time, as Michael J. Greene, operator, and James S. Davis, supervisor.

Davis, according to the report, committed 11 specific errors, including failing to properly examine and close the malfunctioning switch and radioing erroneous reports to central control.

Greene, meanwhile, was alleged to have run his train through an improperly aligned switch and to have failed to press the emergency stop button in the about 15 seconds between the time the car derailed and struck the pillar.

But the report also charged serious misconduct by the staff of Metrorail's control room, naming two men in particular, Kenneth G. Banks and Paul T. Hobgood Jr.

Central control did not ascertain the exact position of the train before giving it permission to back up and did not set up a "permissive block"--a safety precaution in which oncoming traffic is stopped and switches checked--as a train is backed up. Samy E.G. Elias, who is heading the investigation, said that he believes that had the controllers done this correctly, the chain of events that led to the accident would have been disrupted.

In addition, Elias called the attention of General Manager Page to four other "quite urgent" problems that will be examined in detail in further reports.

The first was training. According to Elias, many employes said in interviews that training was conducted too quickly, that there were too few instructors and not enough spare trains on which to practice.

A second was the incomplete shut-down of power. Third rails are equipped with circuit breakers every 500 to 600 feet that act much like household fuses. Short-outs like the one that occurred in the accident, cause the breakers to automatically turn off power in their section of track. However, they turn back on automatically when the problem is alleviated, Elias said.

The derailment triggered one breaker. Elias said that after the accident, technicians in the control room specifically turned off other breakers in the area but did nothing to the one the train had tripped. When passengers alighted and jostled the train, investigators believe, the short circuit was eliminated and the breaker restored power undeneath the train, causing sparks and danger to those present. No one was hurt, however.

In addition, power remained on in a third rail segment in the direction of Smithsonian station, Elias said, for 25 minutes after the accident. Passengers were evacuated through Federal Triangle. "Someone failed to follow through," the report said. "We strongly recommend that an immediate investigation be started . . . . "

The two other "urgent" matters:

Computers that monitor the Metrorail system had activated warning signals in Central Control on 14 different occasions in the three days before the accident indicating that the switch where the accident occurred was out of order. However, no entry was made in maintenance records and no one was sent to fix it until the day of the accident.

Warning that the design of some electrical systems "could have drastic implications in future emergency situations," the report called for immediate creation of a special group to analyze electrical design. It cited boxes in the tunnels that allow emergency power shut-off of third rails but give no clear indication of how much rail each one affects.

Page promised further study of the issues raised by the report. He also ordered that formal disciplinary action, which could range from a verbal reprimand to dismissal, begin against some of those named in the report.

Hobgood, 34, a control room supervisor who was cited for allegedly failing "to provide proper direction to the radio operator for controlling the reverse movement" of the train that crashed, disputed the finding.

"We gave correct verbal instructions, but they were not carried out by the supervisor or operator," he said, referring to Davis and Greene.

Hobgood, who started as a Metrobus driver in 1969 and has been promoted three times in the last 6 1/2 years to reach his current position as assistant superintendent of the subway control room, said the composition of the Metro investigating committee "was unfair as far as we were concerned" because it did not include any control room personnel.

He said the report "was done by people learning to cover their rear end. So therefore the blame was placed on us."

Banks was cited for allegedly failing "to ascertain the location of the train prior to authorizing the reverse movement" of it. Asked whether that was an accurate assessment of his actions, Banks said, "I don't have any comment," and hung up on a reporter.

Supervisor Davis and train operator Greene could not be reached for comment. Davis, whom Metro said was 49 or 50, worked as a bus driver for the defunct D.C. Transit system and later for Metro. He also served as a subway station attendant and a train operator before being promoted to supervisor. Greene, who is 40 or 41, also is a former bus driver and became a train operator in March 1979.