You need to address your question to an attorney in your jurisdiction who handles Federal criminal defense. Most criminal defense attorneys never go to Federal court. Make sure you have an attorney who knows his or her way around the Federal system. Practices vary widely, so it will be to your benefit to speak with someone in your area who knows how these matters are handled.
Under these circumstances, the probation department will likely ask the judge who sentenced you to issue a notice of violation of probation and either a summons or an arrest warrant. The conditions of probation require that the probationer advise the officer of any contacts with law enforcement. If the probationer didn't do so, the officer may add this to the specific violations of probation. When the probationer appears in court, the judge will hold a hearing and determining whether to revoke the probation and sent the probationer to prison, modify the terms of probation or simply restore the probationer to probation. In this hearing, the probationer is entitled to counsel and if indigent counsel will be provided.
In this case, the attorney will have to explain to the court why after almost 3 1/2 years, there were so many violations. If it is because the person started drinking again, there is a chance that the Court will not revoke probation but modify it and add a condition of substance abuse treatment.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.
You should plead not guilty to the new charges. Any plea will automatically violate your probation, and even though you get a light sentence on the new charges, you may get slammed on the probation violation.