* McDonnell Douglas reported a drop of...

* McDonnell Douglas reported a drop of more than 50% in second-quarter earnings Friday, primarily because of costs to develop a new jumbo jetliner and higher expenses for a military cargo plane.

The aerospace company reported earnings of $38 million, or $1 a share, on revenues of $4.9 billion in the three months ended June 30, down from earnings of $77 million, or $2.01 a share, on revenues of $4.96 billion in the same period a year ago.

John F. McDonnell, chairman and chief executive of the company, said its commercial aircraft earnings fell because higher costs to develop the concept of its MD-12, a proposed four-engine jumbo airliner.

He said the decrease in earnings in its military aircraft segment was almost entirely due to a $34-million pretax charge reflecting increased costs and higher reserves in the C-17 program.