The crash of American Airlines Flight 191 as it took off from Chicago yesterday was the worst air disaster in American history, killing 270 passengers and crew members.

The Chicago death toll is nearly double that of the Sept. 25, 1978 midair collision in San Diego of a Pacific Southwest airliner and a small Cessna 172. That disaster killed 144 people.

The worst disaster in aviation history occurred March 27, 1977, when 582 persons died as a result of a collision between two Boeing 747s on a runaway in tenerife, Canary Islands.

The worst single-plane crash in world history was the March 1974 crash of a Turkish DC10 wide-bodied jet near Paris, which took 346 lives.

Yesterday's accident was the second crash of a wide-bodied jet-liner on American soil since their introduction nearly a decade ago. The first was in December 1972, when an Eastern Airlines Lockheed Tristar crashed on approach to Miami International Airport, killing 100 persons.

The worst previous single-plane crash in The United States happened in June 1975, when 113 persons died in the crash of an Eastern Airlines jet near John F. Kennedy International Airport in New York. CAPTION: Map, no caption, By Richard Furno - The Washington Post