I think that a case can be made for the American desire to spread democracy across the world as being ethnocentric. In terms of the strict definition, ethnocentrism represents "the tendency to believe that one's ethnic or cultural group is centrally important, and that all other groups are measured in relation to one's own." This definition can reflect how the American desire to spread democracy around the world is reflective of American perception of government.
Those who advocate for American democracy to spread around the world might do so because they see their own government as working for them. It is here in which the tenets of ethnocentrism exists in the idea that one's own political frame of reference is important enough to supersede others. In its most blunt and direct form, ethnocentrism is most defined and most evident when American proponents of democracy wish to simply usurp current governments and social orders. Accordingly, American involvement that seeks to spread democracy without knowledge of anything indigenous cultural or political identity can be seen as ethnocentric.
At the same time, there are those who could very well argue that ethnocentrism is not intrinsic to the American desire to spread democracy around the world. This line of logic would argue that upholding human values and respect are not ethnocentric. For example, the idea of a constitutionally bound democracy that has been associated with America for over two centuries is not ethnocentric, but rather sound political practice. The American democratic experience of enfranchisement of citizens' right to vote is not ethnocentric as must as respecting universal human dignity. This line of logic argues that embracing values intrinsic to human identity and forming common bonds between individuals is not ethnocentric. It is merely a desire to enfranchise more people. This is not ethnocentric as much as it is seeking to bring more dignity to human life around the world.
A variation of this argument might simply be that even if it is ethnocentric for America to seek to increase democracy around the world, it might not be that bad of a thing. For example, seeking to remove the Taliban from power could be seen as ethnocentric. Yet, the reality could also be that the Taliban sought to repress women and deny voice. American democracy is much more preferable to the Taliban. When Somali warlords starve their people for food, American democracy is simply better than such a condition of being. American democracy would be better from a moral or ethical standpoint than the bloodshed in Darfur. In these situations, some might argue that ethnocentrism might be a byproduct of seeking to make better areas of the world where people are suffering. There are individuals who would argue that American desire to involve itself in spreading democracy might be ethnocentric, but in looking at the alternative, it might be preferable.