NEW DELHI (AFP) - The future of India's govt and a controversial atomic energy deal with Washington hang in the balance this week with coalition facing a trust vote seen as being too close to call. The Indian parliament opens debate on Monday and is expected to decide Tuesday whether the Congress-led government, grappling for support after being ditched by its communist allies, will stay in office. If the government loses, Prime Minister Manmohan Singh will have to resign, and the world's largest democracy will head into national elections " possibly as early as September or October. It will also spell curtains for a deal with Washington designed to bring nuclear-armed and energy-hungry India out of decades of isolation and into the global nuclear energy marketplace. The Congress party says it will win despite the loss of left-wingers, but commentators are not so sure. "Despite all the talk, the vote will be a close thing, as the smaller parties who hold the key may not back the prime minister," prominent political analyst Mahesh Rangarajan told AFP. "One should not be surprised if the government falls by a few votes." The party lost its majority on July 9 when its communist coalition partners withdrew support in protest over the deal, which the left bloc says is too pro-Washington and will derail India's ambitious military programme. The coalition needs 272 votes to survive the July 22 ballot, and projections say it could fall about a dozen deputies short " despite the bullish talk from several top Congress party officials. With the left voting against, Congress has been courting the support of smaller regional and fence-sitting parties. One week ago, Congress said it had won over the regional Samajwadi Party " which has 39 MPs " but some members of that party have threatened to rebel and side with the opposition Hindu nationalist BJP. Rahul Gandhi, the fifth-generation heir of the Nehru-Gandhi political dynasty, has acknowledged the vote could go either way. After all, a previous government lost a 1996 confidence vote by one seat. "For ideological or political reasons the deal is being opposed but the Congress has taken a decision... and sometimes in life, risk has to be taken. If the government falls in the process, so be it," Gandhi said. Rahul's mother and Congress party chief Sonia Gandhi, the Italian-born widow of former premier Rajiv, appealed Thursday to the Indian public for their support over the nuclear deal. "This nuclear agreement is in the best interest of our country and our future generations and I have no doubt they will recognise the value," the party leader told a rally five days ahead of the make-or-break vote. PM Singh shows no sign of rolling back the deal he signed with US President Bush in 2005, saying it is necessary because India's coal reserves of 248 billion tonnes will not last forever. In an oblique appeal to the squabbling MPs, the government's chief scientific advisor R. Chidambaram told a workshop this week "nuclear energy was the inevitable option" for India, which imports 70 percent of its fuel needs. Nuclear power presently accounts for less than three percent of India's electricity generating capacity, according to data obtained from India's Atomic Energy Commission, and the government says that needs to change with soaring oil prices and denting growth levels of around nine percent. Delhi University political scientist Anand Ojha said Congress may have accepted the likelihood of elections coming sooner than May 2009 " the actual end of the coalition's mandate. "This confidence vote is the final dress rehearsal for general elections for all parties," he said.