NEW DELHI, JULY 16 -- Indian Prime Minister Rajiv Gandhi scored a significant political victory today as it was announced that his candidate for the country's presidency, Ramaswamy Venkataraman, had easily defeated his opponents, winning more than 70 percent of the votes.

However, internal rivalries that developed during the indirect presidential election, in which members of the national parliament and state legislatures voted Monday by secret ballot, threaten now to split the ruling Congress (I) party that Gandhi heads.

In a dramatic development tonight, former Gandhi finance minister and defense minister Vishwanath Pratap Singh, a powerful politician from populous Uttar Pradesh state, offered his resignation from the party. If Gandhi accepts, some political observers feel it would establish Singh as the undisputed leader of the national opposition.

Singh, who was once the star of the Gandhi Cabinet, built a reputation as a reformer and populist crusader during his two years as Gandhi's finance minister. In his resignation letter, Singh protested the prime minister's dismissal of three prominent party members, including Gandhi's own cousin, from the Congress (I) Party yesterday. Singh described the dismissals as "undemocratic and dictatorial."

The three men and Singh have all been united recently as undeclared leaders of the dissident faction of Congress (I).

Gandhi supporters allege that all four men were involved behind the scenes in a failed effort to embarrass Gandhi politically in Monday's presidential election. Their strategy apparently was to convince outgoing President Zail Singh, with whom Gandhi has had an ongoing feud, to run for a second term.