A West German scientist said yesterday that an underground nuclear test by the Soviet Union helped touch off last weekend's Iranian earthquake that killed or injured 16,000 persons.

Prof. Heinz Kaminski, director of the West German Observatory at Bochum, said infrared satellite photos showed the Soviet blast created unstable be conditions in the earth's crust that increased the Iranian quake's intensity and acted as a "detonator" to get it started.

The Iranian Geophysical Institute in Tehran denied any link between the Soviet explosion on Sept. 14, and the giant Iranian tremor, about 36 hours later. The Iranian denial was supported by scientists at the Seismological Institute at Uppsala, Sweden, who concluded that the 1,500 miles separating the Soviet blast in western Siberia and the quake-affected eastern border area of Iran made any causal link "hardly possible."

Kaminski, however, said the time difference was about what it would take for the Soviet's nuclear shock to travel that distance along the earth's curst. He called such underground nuclear tests "criminal" and contended that their effects across borders "raise questions under international law."

Shah Mohammed Reza Pahlavi, meanwhile, visited an oasis city devastated by the quake and to mark his grief canceled national celebrations planned for his 59th birthday next month.

The tremor, the worst in Iran's recent history, shattered the city of Tabas, on the edge of the Great Salt Desert, killing or injuring an estimated 11,000 persons. The Red Lion and Sun, Iran's red cross, estimated another 5,000 were killed or injured in surrounding villages and towns.