Sir,
As per rule 2A (i) of Service Tax (Determination of Value) Rules, 2006 if you are able to arrive at the value of service portion of works contract service (AMC service) separately independent of goods supplied while executing the works contract service you can pay service tax @14.5% on the gross value of the service provided by you and you are eligible to avail the credit of duty paid on inputs, capital goods and service tax paid on input services utilized by you for providing the AMC service.
If you are not able to segregate the value of goods supplied and value service provided then under rule 2A (ii) (B) of the above mentioned rule you can pay service tax on 70% of the gross value of the works contract service (value of goods + value of service provided). Explanation 2 of the said rule provides that the provider of taxable service shall not take CENVAT credit of duties or cess paid on any inputs, used in or in relation to the said works contract, under the provisions of CENVAT Credit Rules, 2004. Therefore this rule does not prohibit you from availing duty paid on capital goods and service tax paid on inputs service as credit. The 30% abatement given to you represents duty payable on goods supplied in the execution of works contract. Therefore the explanation specifically debars you from availing the credit on the inputs. This is my view.