A popular anti-corruption crusader who rocked the Indian government with street protests in the summer went on a day-long hunger strike Sunday and has warned of more to come if his demand for a tougher law on graft is not quickly met.

Dressed in a crisp white kurta smock and cap, the bespectacled Gandhian campaigner Anna Hazare said Long Live Mother India as he arrived at the Jantar Mantar observatory, a traditional meeting point for political dissenters in Delhi.

The turnout at Sunday's protest is seen as a barometer of support for the 74-year-old, who has threatened to campaign against the already troubled government in elections in India's most populous state early next year.

By early afternoon, thousands gathered at the venue, as opposition politicians joined in a public debate on an anti-corruption Lokpal (ombudsman) bill that a parliamentary committee has prepared to fight graft across all branches of government.

Hazare says the proposed anti-graft bill is not strong enough, a position backed by the main opposition Bharatiya Janata Party which is seeking to pile on the pressure on Prime Minister Manmohan Singh's Congress-led coalition.

There is no two ways about this that the country needs a strong and effective Lokpal bill, Arun Jaitley, the BJP's leader in the upper house of parliament, told the gathering.

The BJP and other political parties are demanding that the prime minister's office be brought under the ambit of the ombudsman. It is not yet clear whether the draft bill addresses that demand.

Brinda Karat, a leader of the Communist Party of India (Marxist), said the ombudsman must also have the powers to investigate big corporate houses, many of whom have been named in a series of corruption scandals.

The ruling Congress party did not take part in Sunday's debate, which was convened by Hazare. It said it was premature to debate the bill when parliament was seized of the matter.

The spectre of renewed protests in support of Hazare come at a difficult time for Prime Minister Singh, who is increasingly seen as a lame duck just two years into his second term.

Last week, at risk of losing key partners from the ruling coalition, he backtracked on a flagship reform to allow foreign investment in supermarkets.

HUNDREDS GATHER

Hundreds of people with the Indian flag in hand and wearing I am Anna caps, sang patriotic songs as Hazare reached the venue of the strike Sunday after praying at independence hero Mahatma Gandhi's memorial.

Our government takes our money through taxes, through bribes and uses that again to buy votes. How can my grandchildren later say that they are proud to be Indians? said 56-year-old H.S. Kapoor at the protest site.

Hazare has caught the imagination of a swelling middle class in India who are angry at the government's inability to crack down on rampant corruption after multi-billion dollar scams related to telecoms and the 2010 Commonwealth games came to light.

In August, Hazare stopped eating for 13 days, drawing the backing of millions of Indians and forcing the government to agree to create a tough new ombudsman to investigate graft in public office.

But Hazare's image has been tarnished by accusations of financial misdeeds among his top aides, which they deny.

Once strongly supportive, the Indian media has taken a more critical view of Hazare's Gandhian credentials in recent weeks after he appeared to support public flogging of alcoholics, said corrupt politicians should be hung and suggested an elderly politician who was slapped by a protestor had it coming.

The anti-graft bill is likely to be discussed next week by lawmakers and Hazare is adamant it must be passed in the form he wants before parliament closes for the year on December 21.

Several India states go to the polls next year including the country's most important political region, Uttar Pradesh, adding to the political competition.

(Additional reporting and writing by Anurag Kotoky; Editing by Frank Jack Daniel and Sanjeev Miglani)