Here’s a bit about the US past position on India and the NPT. Obviously, this isn’t intended to be exhaustive.
Robert Einhorn explained in this video that the USG had “abandoned” in the early 1990s the idea of inducing India and Pakistan to accede to the NPT as NNWS:
Nevertheless, the US called for universality in 2009 directly in this PrepCom statement. And UNSCR 1887, which the Obama White House touted, “Calls upon all States that are not Parties to the NPT to accede to the Treaty as non-nuclear-weapon States so as to achieve its universality at an early date.” Similarly,, this US presentation to the 2010 RevCon mentions 1887’s support for “NPT universality.” The consensus 2010 RevCon final document also calls for universality.
FWIW, in an ACT interview shortly before the 2010 NPT RevCon, Susan Burk spoke about U.S. policy with respect to India’s nuclear weapons program:
ACT: Has the issue of the U.S.-Indian deal and the broader India deal with the NSG factored in discussions? Has that been raised by countries in discussing obligations they need to assume and responsibility under the NPT?
Burk: Yes. It gets raised frequently in NPT discussions, and our response is that it was seen as a way to bring India closer to the nonproliferation norm, to an agreement that would in the end bring more of their facilities under safeguards. That was the motivation. But it does come up frequently in discussions.