Heart attacks continue to be the major killer of firefighters who die in the line of duty, a nationwide study said Thursday.

Fifty-eight of the 126 firefighters who died on the job in 1987 suffered heart attacks, according to a National Fire Protection Association survey.In each of the 11 years of the study, except 1984, heart attacks was the leading cause of death among firefighters.

The total number of firefighter deaths last year was the highest since 1981, when 134 firefighters died, according to the report. In 1986, there were 113 deaths.

Other causes of death were internal trauma, which claimed 28 lives; asphyxiation, 13; and crushing, 12, the survey showed.

The study said more than half of the deaths - 73 of them - occurred when firefighters were responding to or returning from fires, or during training or administrative duties. Fifty-three deaths occurred on the scene of the blaze, the study said.

The majority of deaths suffered on the scene occurred at wildland fires, including forest fires.