After weeks of review of a troubled Baltimore factory, federal regulators have decided that about 60 million doses of the Johnson & Johnson coronavirus vaccine produced there must be discarded because of possible contamination, according to people familiar with the situation. The Food and Drug Administration plans to allow about 10 million doses to be distributed in the United States or sent to other countries, but with a warning that regulators cannot guarantee that Emergent BioSolutions, the company that operates the plant, followed good manufacturing practices. The agency has not yet decided whether Emergent can reopen the factory, which has been closed for two months because of regulatory concerns, the people said. For weeks the F.D.A. has been trying to figure out what to do about at least 170 million doses of vaccine that were left in limbo after the discovery of a major production mishap involving two vaccines manufactured at the site.