A subway worker was electrocuted early today on elevated A line tracks in Queens after he tripped on a segment of slick, wet track, transit officials said.

James Knell, 45, died at 4:30 a.m. after he tripped and fell on the third rail at the Beach 90th Street Station in Rockaway Beach.

While it appeared that Knell’s death was an accident, NYC Transit launched an investigation to “determine a cause and to ensure we prevent a recurrence,” said NYC Transit President Tom Prendergast.

Knell, a supervisor and NYC Transit employee for 13 years, was part of the crew working on a station rehab project.

“We lost one of our own this morning and labeling this incident a tragedy is a painful statement of the obvious,” said Prendergast.

Knell was replacing track panels when he was killed.

John Samuelson, president of Transport Workers Union Local 100 who said he had worked together with Knell in the past, argued that no transit worker should be near a third rail while it rained.

“Nobody should be working near a live third rail while its raining or wet. You can clearly be killed,” he said.

Samuelson said he would seek a rule change so that this “will not happen again.”

He added that the “third rail was turned off during the work. It was then energized at the end of the job to run a test train. Jimmy then went back on the tracks to retrieve a bucket. It was wet, and he slipped and fell onto the third rail. Water and an electrified third rail don’t mix well.”

Knell was a resident of East Rockaway, LI, and is survived by his wife and two step-children.

Prendergast said Knell is the first transit worker to die on the job in three years.

Service on the A was temporarily suspended. Riders were forced to take shuttle buses during the morning commute from the Beach 67th Street Station.