Birth Cert. name vs. name I've used all my life?

I live in Oregon and was born in California. On my birth certificate I have the name Mary Bernadette ________(& last name). My mother changed my name through infant baptism to Monica Jean_____, which is on my baptismal certificate and is what I have used as identification all my life. I want to get a passport and I'm not sure if I need to legally change my name to Monica Jean (which I've used on everything from drivers lic. to SSN.) or just use the baptismal certificate (if acceptable) when obtaining my passport? If I have to change my name, how do I go about it and what type of attorney do I go to, in order to do this?

Thank you,