The Metro Board, hoping to prevent a repeat of the January subway derailment that killed three people, yesterday authorized a $200,000 consultant's study of how people, computers and trains interact in running the highly automated Metrorail system.

Carlton Sickles of Maryland, head of a board panel investigating the derailment, said the accident's immediate causes have been corrected already. But he said that detailed, outside analysis of whether humans and machines may be working at cross purposes could further ensure safety.

Trains stop, start and keep from running into each other through commands from a computer in the basement of Metro's headquarters on Fifth Street NW. This would be the first time since trains began running in 1976 that Metro has taken a detailed look at how people fit into this "Automatic Train Control" system.

Investigators studying the Jan. 13 derailment, Metrorail's first fatal accident, have reported numerous cases of human error in the control room and at the crash site between the Smithsonian and Federal Triangle stations. Current equipment and ways of working may make unreasonable demands on employes, Metro officials believe.

For instance, control room personnel now use diagrams generated by computers on cathode ray tubes to follow the movement of trains. Study may show these images tire the eye, leading people to miss hazardous developments, according to Sickles. "On that day, apparantly certain things were bleeping on the computers but were not registering" on controllers, he said.

Other areas the study will cover are control room layout, the duties of different people in the room, the chain of authority and how the controllers communicate with train operators and with the computers.

In addition, Sickles' safety group also wants a major study of emergency procedures, though it did not ask the board for a decision yesterday. It is also requestng that the board consider proposals that Metro educate passengers on how to get out of cars during an emergency.

Doing so would reverse a longstanding and much-debated philosophy that passengers should not know how to get out, on the grounds that pranksters might misuse the knowledge, that people might panic and jump out in noncritical situations and that the 750-volt "third rail" in the tunnels can present a bigger danger than things inside the cars.

In other action yesterday, the board:

* Voted to award a $17 million contract to the Chicago-based Seven K Construction Co. to build the Vienna rail station, the terminus of the Orange Line, and one mile of right-of-way down the Interstate 66 median. When work begins, it will mean that the entire western leg of the Orange Line is under construction, with service scheduled to begin in 1986.

* Voted to continue L5 Metrobus service linking Potomac Park and Chevy Chase Circle on an experimental basis for another six months. Metro had proposed eliminating the route altogether after the Red Line was extended to the Van Ness-UDC station last December, but political opposition led to its retention while ridership and revenue were evaluated.

* Voted to cut service on the 6P route between the Pentagon and Park Center in Alexandria from 12 to seven trips daily starting in January next year. Low ridership was cited for the decision.