By Kristin Roberts

NEW DELHI (Reuters) - The United States and India will study the possibility of a joint missile defence system, U.S. Defence Secretary Robert Gates said on Wednesday, stressing talks were only in their early stages.

"We're just beginning to talk about perhaps conducting a joint analysis about what India's needs would be in the realm of missile defence and where cooperation between us might help advance that," Gates told reporters.

Indian missile-defence cooperation with the United States could complicate relations with China, Russia and Pakistan.

Until now, India's policy has been to develop its missile shield domestically, closing a potential multibillion-dollar market to American manufacturers Boeing, Lockheed Martin, Raytheon and Northrop Grumman -- the biggest players in the emerging ground, air, sea and space based U.S. missile defence system.

But this may be changing in line with a breakthrough Indian decision to buy Lockheed's C-130J military transport aircraft earlier this year, U.S. defence officials said.

Gates, in New Delhi to strengthen Washington's strategic ties and make a sales pitch for U.S. arms manufacturers, said the Pentagon wanted to build a relationship focused on long-term cooperation with India, noting it was independent of the current impasse over a controversial civil-nuclear deal sought by Washington.

"We're not looking for quick results or big leaps forward," Gates told reporters.

"But rather a steady expansion of this relationship in a way that leaves everybody comfortable that we're not moving too fast and that works in terms of Indian domestic politics and also works for us.