Sonia Gandhi, who led her party to an upset victory in parliamentary elections despite the handicap of a foreign birth certificate, stunned the nation Tuesday by telling a chaotic meeting of her supporters that she would not accept the job of prime minister.

The Italian-born leader of India's Congress party delivered her decision amid tearful and anguished pleas that she reconsider. Her announcement followed protests by Hindu nationalists, who said Gandhi's origin made her unfit to be prime minister in a country where memories of colonial rule are still fresh. Gandhi, 57, the inheritor of a three-generation political dynasty, had been widely expected to take office later this week.

While Gandhi did not propose an alternative candidate, officials from Congress and allied parties said they believe she favors Manmohan Singh, a Cambridge-educated economist who served as finance minister under a previous Congress government, from 1991 to 1996. Gandhi will keep her seat in Parliament as well as her leadership role in the party, which will give her considerable influence over the new government, analysts said.

"For the six years that I have been in politics, I have said it many times that the place of the prime minister is not my aim," Gandhi said Tuesday evening in Parliament's central hall, struggling to make herself heard over shouts of dismay from Congress lawmakers. "I was always certain that if ever I found myself in the position I am in today, I would follow my inner voice. I humbly decline the post."

Associates said that Gandhi was rattled by the vehemence of the Hindu nationalists' opposition and influenced by her two grown children, Rahul and Priyanka, who feared that their mother's life would be in jeopardy if she assumed such a high-profile position.

Last Thursday, results from elections that had been spread over three weeks showed that Congress and its allies had soundly defeated the Hindu nationalist Bharatiya Janata Party (BJP), led by Prime Minister Atal Bihari Vajpayee, in contests for the 545-seat Lok Sabha, or lower house. The BJP and Vajpayee had led the coalition that governed India since 1998.

In the days since the election results were announced, Gandhi had been coy about her intentions, never publicly declaring that she would seek the prime minister's job but doing nothing to discourage the idea. On Saturday, Congress elected Gandhi its parliamentary leader, a post customarily held by the prime minister. Leaders of parties aligned with Congress, including India's two main communist parties, subsequently said they would support Gandhi and her coalition but would not formally join the government.

The prospect of a government in which communists would play a prominent role rattled the Bombay Stock Exchange, which suffered one of the largest drops in its history Monday. It recovered slightly late in the day after Singh, the former finance minister, reassured investors that the new government would not reverse the process of economic liberalization that began when he was in government in the early 1990s and gathered steam under the BJP-led coalition. News of his possible selection sent stock prices sharply higher Tuesday.

But the most vocal reaction to the new government had come from the BJP and its allies in the family of Hindu nationalist organizations known collectively as the Sangh Parivar. BJP leaders in Parliament said that they would boycott Gandhi's swearing-in ceremony, although Vajpayee would attend, and that they would lend their support to a national protest movement against Gandhi.

Sushma Swaraj, Vajpayee's health minister, threatened to resign her seat in Parliament, shave her head and wear white -- the color of mourning in India -- if Gandhi became prime minister.

"Only 57 years ago, we have thrown the firangi out of India," Swaraj told the private television channel NDTV on Tuesday, using the Urdu word for foreigner. "Today we are crowning her with our own hand? Is it not a matter of shame?"

Rumors that Gandhi might back away from the prime minister's job began circulating Monday evening. Congress leaders dismissed those reports. But by midafternoon Tuesday, as word of Gandhi's decision seeped out, hundreds of Congress workers gathered outsider her official residence to beg her to change her mind. Some wrote pleas in their own blood. One man waved a pistol, held it to his temple and threatened to kill himself if she did not reconsider.

Some Gandhi supporters blamed the Hindu nationalists for her decision. "It's a sinister attempt to nullify the popular vote," Somnath Chatterjee, a senior leader of the Communist Party of India (Marxist), or CPI(M), told reporters. "It is nothing but a day of shame for this country that the elected leader of the largest party cannot form a government."

But others cited the role of Gandhi's children in her decision. "If the children say we have lost our father and we don't want to lose our mother, what can we say about it?" asked Jyoti Basu, another senior CPI(M) leader.

Gandhi's son, Rahul, who last week won his first parliamentary seat from a district in the state of Uttar Pradesh, told reporters Tuesday night that he was not surprised by his mother's announcement. He recalled that when he asked her last week whether she would take the prime minister's job, she replied, "Whatever I have been thinking for the last six years, the same thoughts are on my mind even today."

Rajiv Shukla, a Congress minister of parliament who is close to Sonia Gandhi and her children, said in an interview Tuesday that the Congress leader had always been ambivalent about the job.

"Her mission was always to fight and bring the party back on its feet, bring the party to power, and then stop short," he said. "But she went through the whole motion to get the structure of the government alliance in place, to unify all the partners. Only she could have done it."

After Gandhi made her announcement, a succession of Congress lawmakers delivered emotional speeches. "Not a single person here thinks that anybody else is entitled to be the prime minister," said Kapil Sibal, a senior Congress parliamentarian from New Delhi. "We respect your sentiment. That does not mean we expect it. Please reconsider."

The party then passed a resolution making the same request, deferring for now the question of whether to anoint Singh prime minister in Gandhi's stead. But Gandhi once again declined, apologizing for "your pain, your anguish, at the decision I have taken."

Communist leaders and other Congress allies have indicated they would support Singh, 71, a self-effacing former university professor who has held a number of economic policy jobs over several decades in government. By virtue of his role in promoting economic reform during the last Congress government, he also has won the confidence of many in the business community. As a Sikh, Singh wears a light-blue turban and would be the first member of an Indian religious minority to hold the prime minister's job.

Gandhi is the widow of former prime minister Rajiv Gandhi, the daughter-in-law of Indira Gandhi, who served twice as prime minister, and the leader of the Congress political dynasty that began with Jawaharlal Nehru, India's prime minister from 1947 to 1964. Rajiv Gandhi and his mother were assassinated in separate attacks.

Sonia Gandhi, a builder's daughter from northern Italy, met Rajiv Gandhi in the late 1960s while studying English in Cambridge, where he was a university student. She became an Indian citizen in 1983. As the head of the Congress party, she has often described herself as the guardian of the Gandhi family's legacy, especially its commitment to the secular values that were a hallmark of Nehru's leadership.

Special correspondent Rama Lakshmi contributed to this report.

Sonia Gandhi cites "inner voice" in turning down India's premiership.