Third oil crisis by 1990 seen by energy expert

A third oil crisis is likely before 1990, and petroleum prices may double by the year 2000 - events that could be tougher on America than the Great Depression, a Harvard University energy expert, warned.

Daniel Yergin spoke at a press conference for the new book ''Global Insecurity,'' written by him and Martin Hillenbrand, a foreign affairs expert and former US ambassador to West Germany.

Dr. Yergin criticized the Reagan administration's energy policies, citing the President's embargo against the Soviet natural gas pipeline as a blunder that shows the administration's ''spirit of energy isolationism.''

Meanwhile, President Reagan denied reports the administration is considering easing its ban on equipment sales for the Soviet pipeline.