NEW DELHI (AFP) -- India's Congress party chief Sonia Gandhi was all set for a landslide victory Monday in a by-election she provoked by resigning amid charges of wrongfully holding two salaried posts.

The widow of India's assassinated former prime minister Rajiv Gandhi was contesting her Rae Bareli parliamentary constituency where voting was underway in the politically strategic northern state of Uttar Pradesh.

The Italian-born 59-year-old is the standard-bearer for India's high-profile political dynasty created by founding prime minister Jawaharlal Nehru and continued by his daughter Indira Gandhi, mother of Rajiv.

But Gandhi's victory has always been considered a "foregone conclusion," said Rashid Kidwai, Sonia Gandhi's official biographer.

Her March 23 resignation took the sting out of a political storm that had threatened to engulf Congress over senior figures holding multiple government posts.

Only the margin of victory over her main challenger, the Hindu nationalist Bharatiya Janata Party's Vinay Katiyar, has been open to debate.

"It's an open-and-shut case," said political analyst Mahesh Rangarajan, a visiting professor at Cornell University in the United States.

"What we have to see is the size of the majority -- she won by 240,000 votes last time -- we have to see if it goes up or down," Rangarajan said. "I think it will go up because they have put in a lot of effort."

The campaign saw Gandhi's children, political heir-apparent Rahul and his sister Priyanka, spearheading a publicity blitz.

Kidwai said, however, that the victory would be more a symbol for Congress.

"A landslide win is not expected to put a stop to the Congress party's declining fortunes" in India's most populous state, with 80 members of Parliament, he said.

Rae Bareli has been the electoral bastion of India's charismatic Nehru-Gandhi dynasty for decades and Gandhi swept the seat in 2004.

India's constitution disqualifies an MP "if he holds any office of profit under the federal government or government of any state, other than an office declared by the national legislature by law not to disqualify its holder".

The by-election coincides with millions of Indians voting in the final phase of elections to several state assemblies -- seen as a referendum on the federal Congress-led government as it approaches two years in power.

The Marxist bastion of West Bengal, the southern state of Tamil Nadu and the union territory of Pondicherry also went to the polls Monday.

Voting in northeastern Assam and the southern state of Kerala is complete and results for all five states will be announced on May 11.

In West Bengal, security has been stepped up after complaints by opposition parties of fraud and intimidation during four previous stages of the staggered elections.

"Federal paramilitary forces will be deployed in all 49 constituencies going to the polls," said Raj Kanojia, state police chief.

More than eight million people are eligible to vote for 306 candidates in the state, where a communist government has been in power since 1977.

Left-leaning political parties were expected to return to power in West Bengal and to defeat the ruling Congress-led coalition in Kerala, opinion polls said.

In Tamil Nadu, the two main regional fronts were locked in a fierce competition to woo voters, promising gold for women planning to marry and computers for students who passed certain examinations.