NEW DELHI (Reuters) - Opposition lawmakers shut down the Indian parliament on Monday after demanding that Delhi's chief minister quit over graft allegations, the third enforced closure since it reopened last week. As well as disrupting business, the closure put India's coalition government even further on the defensive as it struggles to push a reformist agenda. The opposition Bharatiya Janata Party (BJP) wants the resignation of Sheila Dikshit, a stalwart in the ruling Congress party, after a state auditor slammed costly tenders given to questionable contractors for the 2010 Commonwealth Games on her authority. Dikshit has denied any wrongdoing. The ruckus is the latest in a string of corruption scandals to plague Prime Minister Manmohan Singh's second term in office, denting his government's credibility as it tries to maintain growth in Asia's third-largest economy. The parliamentary shutdown may scupper plans to introduce reform bills, including one to make it easier for industry to acquire land, that were blocked in the previous session amid similar opposition protests. A poll by the Centre for the Study of Developing Societies (CSDS) published in the Hindu newspaper on Monday showed the number of people who think Singh should continue in office fell to 22 percent from 40 percent during his first term in 2006. Graft scandals have hit the country at a time when its economy is showing signs of slowdown, grappling with high inflation and a series of rate hikes by the Reserve Bank of India (RBI), against a background of global economic uncertainty. "It's a lame duck government and a lame duck parliament, it has reached that point," said N. Bhaskara Rao, chairman of New Delhi-based think-tank Centre for Media Studies. "That being the case, one needs to worry that the global economic trend being what it is, how are we going to cope with that, with the declining stock markets." Indian shares fell to their lowest level in more than a year on Monday following news that Standard & Poor's has downgraded the United States' sovereign debt rating. That prompted Finance Minister Pranab Mukherjee to say India's growth story remained "intact". Members of the BJP, wearing traditional long white shirts, crowded the speaker on Monday, shouting "remove Sheila Dikshit" while the speaker sat smiling patiently. The sight has been a familiar one of late. The Congress party-led government is trying to push landmark reforms including those of land acquisition and taxation, aiming to liberate industry from the country's notoriously slow bureaucracy, but instead graft scandals have disrupted parliament for much of the past year. Singh has tried to fend off accusations he is a lame duck leader, and combat a widespread feeling Congress has run aground politically. The head of the party, Sonia Gandhi, is undergoing surgery abroad, which could hasten her son Rahul's accession to power. In the CSDS poll, 19 percent of respondents favoured Rahul Gandhi as the next prime minister compared to 10 percent for Singh. In 2009, the year of Singh's re-election, he led Rahul as the number one choice for the job by 18 percent to 6 percent.