This is an important question. One of the unique characteristics of American culture and law, which I think is great is that there is a separation between church and state. I hope that this continues. Because of this, the government does not interfere with matters of faith. So, if a person want to use the words: "In the name of God, the compassionate, the most merciful," he or she can do so.
With this stated, there are a few nuances. If a person wants to teach a particular religion in a public office or as a teacher, they would not be allowed. Why? The church would be encroaching into the realm of the state. So, just as the state does not encroach in matter of religion, the church must not encroach in matters of the state.
By and large, there is freedom of expression and religion.
No is it not forbidden. Religious freedom allows for people to express their individual beliefs. However, making such a statement could very easily cause problems if it seems like someone is imposing their beliefs on someone else, especially in some areas such as politics or in public schools.