In the comic strip "Doonesbury," it was whimsically called "dumpster-diving." But a group of Minneapolis doctors, writing in The New England Journal of Medicine, reports an increased number of real injuries to homeless people falling into or out of trash dumpsters.

Dr. Richard T. Zera and several colleagues at the Hennepin County Medical Center said these three cases occurred in a three-month period last year:

*A 31-year-old man suffered a deep cut to his right hand while trying to pull himself into a dumpster. Although he could not bend his right index finger, suggesting a cut tendon, he left the hospital, refusing further treatment.

*A 53-year-old woman scavenging through a dumpster fell into the street, damaging her right knee. After six months, she is still recovering from treatment, which included surgery.

*Emergency room doctors found two shards of glass in the back of a 36-year-old man who fell backward into a dumpster. The glass was removed and he recovered.

One other homeless person was less fortunate, they report. In St. Paul, a 30-year-old man apparently fell asleep in a dumpster "and was killed when it was emptied into the back of a trash truck."