Indian Civil Accounts Service (ICAS) is an accounting service that primarily deals with the accounting function of the civil ministries of the central Government. The Ministries that fall outside this categorisation ( Defence, Railways, Post and Telecommunications) have their own accounting services.
Indian Defence Account Service has a history of its own and is one of the oldest civil services to have been there. It is one among the colonial services.
The ICAS was created in the 1970’s during Indira Gandhi’s time, taking away the accounting function ( of Union Government) from the IAAS. One argument that is lined in favour of this separation of auditing and accounting functions is the conflict of interest arising from the accountant himself being the auditor.
There is an alternate version to this story of the ICAS being separated from IAAS. It is said that her electoral malpractice was proven using the records provided by the Accountants General (AG), Allahabad and Indira Gandhi, took it out on the IAAS by taking away its Accounting function of Central Government. The fascinating story behind this can be read in the memoir of Dy. CAG (Retd.) Parimal Brahma. (The Theatre of the absurd: On the corridors of power).
Whatever be the story behind it, IAAS is rather happy to have the accounting function taken away from it. Despite the name having “Accounts” in it, the service is primarily concerned with assisting the CAG with his auditing function. The reason for not merging the three Accounts Services (IDAS, ICAS and IPTAFS), I believe, is because of legacy issues.
Coming to the differences, IAAS officers are under the adminstrative control of the CAG and has auditing functions, primarily. In most of the States, the accounting function of State government also lies with IAAS. The job is thus a mix of Accounting and Auditing, with a lot of deputations available in the Central Government in various roles. There are also many opportunities to audit many international bodies too.
In the Accounting Services, you will primarily be dealing with Accounting functions of the respective authority, which would make up a major chunk of your career. There are also many deputations in the Central Government in capacitied like Financial advisor.
As for which service is better, in the following aspects, I would say that IAAS is better. It has a wider ambit, job diversity, promotional prospects and autonomy. If you want to give the Accounting services above IAAS in your service preferences, I would advice you to think again.