Accountants in the United States fall into two categories, Certified Public Accountants and non-certified accountants in private employment. Needless to say, the former category is highly compensated and enjoys better employment prospects. If you desire to acquire certification, you must pass a licensing exam [CPA exam conducted by the AICPA]. Please visit http://www.aicpa.org/BecomeACPA/Pages/BecomeaCPA.aspx for further information. You could enter the United States to give the exam as a visitor [on B-1 or B-2 visa].
Once you have decided you career goals and objectives, you will have to apply for employment in the United States. The employer can then sponsor you on an H-1B Nonimmigrant Visa [dependents can enter on H-4 visa]. This visa category will enable you to enter, stay and work in the United States for a period of up to 6 years. During your stay in the United States, you could have your employer process a Green Card Application on your behalf. This will entitle you to remain and work, permanently, in the United States.