The Reagan Administration has dropped rules that prevented American companies from sending aloft satellites that could produce highly magnified pictures of objects on Earth, according to a published report. The change was included in an updated national space policy signed by President Reagan on Jan. 5 but was not made public at that time, the New York Times reported in today's editions. It would allow advanced American satellites that could produce high-resolution pictures for use by scientists, geographers, journalists and others. The government previously has barred private companies from operating satellites that could produce pictures showing objects smaller than 10 meters across. But the Soviet Union markets worldwide satellite photographs with a resolution of five meters, and French companies have satellites that produce pictures nearly that clear.