A 30-year-old Northwest man was fatally injured yesterday after he fell or jumped from the Duke Ellington Bridge while workers were erecting a suicide prevention barrier that D.C. Mayor Marion Barry ordered built there last month, D.C. police said.

They said that the man, who was not immediately identified pending notification of relatives, went off from the south side of the bridge about 4:30 p.m. while three workers, on the opposite side of the bridge, were completing a portion of the eight-foot-high barrier.

Police said last night that the man plunged from an area of the bridge where the fence had not been completed. He landed on a grassy area near the shoulder of Rock Creek Parkway and suffered multiple fractures and massive head injuries, they said. He was taken to George Washington University Hospital where he died about two hours later.

Police said that the death was an apparent suicide, but an official ruling from the D.C. medical examiner's office is expected today.

In less than eight years, 37 persons, including at least eight last year, have jumped from the Ellington Bridge and the nearby Connecticut Avenue span over Rock Creek Park.

Construction of the suicide prevention barrier began last September but was halted by Barry after community leaders and preservationists argued that it would not prevent suicides, and would spoil the scenic view from the bridge.

Late last month after other persons fell from the bridge, Barry ordered that the barrier be completed.