The Federal Aviation Administration is moving to prevent repetition of the mistake that caused a Delta Air Lines pilot to turn off both engines and send his plane plunging toward the Pacific Ocean.

The agency's Seattle office has given airlines 10 days to install a guard over the fuel-cutoff switch, which the captain of Delta Flight 810 told federal officials he mistakenly hit shortly after takeoff from Los Angeles Tuesday.

The error caused the Boeing 767-232, bound for Cincinnati with 205 persons aboard, to plunge an estimated 1,000 feet to within 600 feet of the ocean. The captain, who has not been identified, told National Transportation Safety Board investigators that a warning light indicated a problem with the right engine's electronic control.

He said he intended to switch to manual throttle control by hitting the electronic engine-control button next to the fuel-cutoff switch.

FAA spokeswoman Judy Nauman said yesterday that the switch guard was ordered as an interim measure while the agency explores a more permanent solution, such as ordering redesign of instrument panels.

Nauman said a United Airlines pilot made a similar mistake, shutting off fuel after taking off from San Francisco on March 31, 1986.

The order affects all of the approximately 75 U.S.-registered Boeing 767s and about 30 Boeing 757s equipped with Rolls Royce RB211 engine, she said. Trans World Airlines, American Airlines, United and Delta fly 767s, and Eastern Airlines and America West fly 757s with the RB211 engine.

Boeing spokesman John Wheeler said the switch modification is simple and can be performed at an airport. "I'm sure our guys are considering what {permanent} changes can be made . . . . "