The official told The Associated Press that the first of some 4,000 soldiers had begun arriving in the state capital, Morelia, to prepare for an offensive in a mountainous western section of the state known as Tierra-Caliente. The area has been hit by a surge in violence in recent weeks.
The official spoke on condition of anonymity because he was not authorized to release the information. A military spokesman declined to comment.
The deployment is the largest in Michoacan since July 2009, when some 5,500 troops and federal police arrived.
Authorities in Michoacan are battling quasi-religious drug cartels called La Familia and the Knights Templar that claim to be following divine will.
Officials said at least 56 people were slain in the state last month during at least 10 battles between criminal gangs and law-enforcement officers. The violence has been most prevalent in Tierra-Caliente.