David Shear says without support from Myanmar's military, the transition to democracy "will likely falter."
He was responding in writing to questions posed for his Senate confirmation today to become assistant secretary of defence for Asian and Pacific security affairs.
The US has initiated military dialogue with Myanmar on human rights and military law, hoping to encourage reforms, but has faced congressional opposition to expanding ties.
Shear said the US should be "clear-eyed" about the Myanmar military's poor rights record and history of dominating politics, and any expansion of defence ties requires progress on democratisation and ending military trade with North Korea.