Rajiv Gandhi, a soft-spoken man with a gentle nature, came to politics unwillingly. Yesterday, following the assassination of his mother, Indira Gandhi, he became the third person in his family to hold the Indian prime ministership.

Rajiv Gandhi, 40, was sworn in by Indian President Zail Singh within hours of the death of his mother, who had led India for 15 of the past 18 years. The decision on the prime minister's succession was made in a hastily called emergency meeting of all the government's Cabinet ministers.

In June 1980, Rajiv had been a contented pilot for Air India, unconnected to politics, when his flamboyant brother, Sanjay, died in the crash of his stunt plane.

A grief-stricken Indira Gandhi and the leaders of her party pleaded with Rajiv to run in elections for the seat Sanjay left vacant in the Lok Sabha, the lower house of the Indian Parliament.

Rajiv, the older son, who then was 36, allowed himself to be persuaded to enter the political arena, with misgivings that his friends described at the time as grave.

"The way I look at it is that Mummy has to be helped somehow," Rajiv was quoted as saying shortly after his brother's death.

"She had a lot of support from Sanjay and now it's not there. I can't really give her the sort of support he was giving her," he said. "I don't know anybody, I don't know much about politics, so there's no question of my stepping into his shoes."

Rajiv made no secret of his doubts about taking his brother's place as representative from the Amethi district in Uttar Pradesh, India's largest state, and as heir apparent in the Gandhi line of succession.

Further, he readily admitted, he was hesitant to give up the quiet life he and his Italian wife Sonia led with their son Rahul and daughter Prinyanka in a broad-lawned suburb of New Delhi. But Rajiv capitulated, and after a strenuous campaign was elected to Sanjay's seat in 1981.

His mother named him one of the ruling Congress-I (for Indira) Party's general secretaries in 1983, and the post of second in command followed.

At the time, the apparent attempt to ensure a Gandhi succession brought howls of protest from opponents and supporters alike. On both sides of Parliament it was said that Rajiv was politically weak, and his foes cited as proof his inability to say no to "Mummy."

The more serious charge was that Indira Gandhi -- whose father Jawaharlal Nehru was the first prime minister of the world's most populous democracy -- was attempting to set up a dynasty.

She held tenaciously to political control over her party, and Rajiv has developed little base of his own. Most of Sanjay's political support -- primarily among India's young political leaders -- transferred automatically to his mother after his death.

Some Sanjay supporters who wished for an alternative to Indira Gandhi's tight control have embraced Maneka Gandhi, Sanjay's widow. The fiery young woman broke with the family after her mother-in-law Gandhi accused her of consorting with political enemies.

In 1982, Indira Gandhi ordered Maneka to leave the family house, where the prime minister was shot to death yesterday, and Maneka formed her own party.

Maneka has challenged Rajiv for the Amethi seat in elections scheduled to be held by the third week of January. Her party, the Rashtriya Sanjay Vichar Manch, which translates literally as the Sanjay Thought Platform, has made impressive gains in recent regional elections, and many political observers believe she has a good chance of winning the seat.

Since his election, the tall, balding Rajiv has been more forceful in his efforts to influence policy in what has been viewed as an attempt to prove that he has acquired political maturity.

In charge of party organization, Rajiv has surrounded himself with young professionals, very unlike most Congress-I politicians who have gained political power by rising through party ranks.

Rajiv and his advisers, Indian versions of young, upwardly mobile professionals, have been the butt of many jokes made both by old Congress-I faithfuls and opponents of the younger Gandhi.

Rajiv's approach, which employs forecasting models and other modern management methods, has been ridiculed as too new-fangled for India. His fondness for using a personal computer, in a nation where electricity can be an elusive commodity, has been the source of much humor in the Indian news media.

Rajiv, who was educated at Cambridge, also has taken Hindi diction lessons to change his image as an Anglicized Indian with little feeling for the common man.