Notice Period - in the letter of appointment is of 2 months and in handbook of the company it is mentioned as 1 month

In case, if the notice period mentioned in the letter of appointment is of 2 months and in handbook of the company it is mentioned as 1 month, which will be valid?

The letter of appointment is a document issued to you and accepted by you, so it is more binding in nature. But, in case it is so provided in the appointment order that you will be governed by the rules and regulations as amended from time to time and the Handbook is a subsequent document, then there is a case that it will be applicable.