India should be the ally of US if it not for the war of terror where US constantly arms and funds Pakistani Army. This itself reflects the complicated relationship, I think India will always overtly reject the idea of being lynchpin to America's strategy, but covertly be accept the role.
Naa, as far as being an ally, I would say no to it. Its funny how people easily relate things we have only bought weapons/aircraft of few billion dollars which are nothing if you compare to the deals with Russia/France and Israel, yet people think India is helping US. As far as US goes, India should keep its distance make sure they stay on their side, the things we need are newer technology and the bans to be lifted. As for US role in Afghanistan they can deal with that on their own with the help of NATO and their true allies. India has been fighting these terrorists for a long time now and have done a great job in doing so we don't need US help in it.