The crash of a Florida-bound jetliner into the icy Potomac River on Wednesday was the third, not the second, fatal accident involving commercial passenger aircraft at National Airport since its opening in 1940.

Further research yesterday recalled the crash on Dec. 12, 1949, of a Capital Airlines DC3 into the Potomac River while approaching the airport from the south in heavy rain and fog. Four people, including the pilot and copilot, died in the crash and two other persons died later of injuries.

That crash followed by six weeks the midair collision of an Eastern Air Lines DC4 with a war surplus fighter plane that killed 55 as both were approaching National, also from the south.

William L. Stevens of Bethesda, a survivor of the Capital Airlines crash, reminisced about the mishap in a telephone interview yesterday. A civilian employe of the Navy at the time, he said he was coming home from Newport News, Va., when the plane plunged into an inlet of the river south of the airport.

"I was knocked out from the cold," he said. He and 18 others were plucked from the river by crash boats dispatched from Bolling Air Force Base.

A federal investigation later found that the plane's two engines stalled, and blamed the mishap on pilot error. Capital Airlines, operator of the plane, was later merged into United Air Lines.