NEW DELHI (Reuters) -India is opening up a chunk of its protected government procurement market to foreign firms, including the U.S, two government sources said, in a shift that could extend to other trading partners after it was offered to the UK under a trade deal this month. The government is likely to allow U.S. firms to bid for contracts worth over $50 billion, mainly from federal entities, as it negotiates a trade deal with Washington, the sources said. Total public procurement - including by federal, state and local governments and state-run firms - is worth an estimated $700 billion-$750 billion per year, according to government estimates.