What's equivalent of IAS in United States

Is there much difference. Is their system somewhat better. Does we need to make any changes.

No, there is no such thing in USA. "Does" we need to make any changes? Yes. We need to stop aping them. We need to change our mindset that whatever they are doing is good for us too.

USA and India are different. What they are is because of their history, their geography, and demography. One cannot Copy and Paste that to their own country.

Having said that, let me answer the question. USA has a "spoils system". Whichever party is in power, it choses its own people for the higher offices. A banker may become treasury chief and vice-versa. There is no permanent civil service like IAS. President can chose anybody to head a department. He need not be from the government.