Shortly after the 12-day period of state mourning for assassinated prime minister Indira Gandhi ends Monday, her son and successor, Rajiv, will begin an appeal to 400 million Indian voters to ratify his heritage to the dynasty of the House of Nehru.

Gandhi, a relative political neophyte, is expected to launch his first major electoral campaign to coincide with the 67th anniversary of his mother's birth on Nov. 19, and from all outward appearances, it will be an unabashedly sentimental entreaty to the sympathies of a grieving nation.

While a date for the parliamentary elections has not yet been announced officially in deference to the mourning period, the new prime minister has quietly made it clear through senior advisers that the polling will be held on schedule in time to constitute a new Parliament by Jan. 20, and that the end of next month or the first week in January is the most likely time for balloting.

Paradoxically, before Indira Gandhi's assassination, her ruling Congress (I) Party appeared headed for a major setback -- at best a reduced majority in the principal chamber of Parliament, the Lok Sabha (People's House), and possibly even being forced to join a coalition to retain power for the next five years.

Bedeviled by sectarian violence in widely scattered parts of the country, Indira Gandhi had appeared on the defensive for the first time since her political comeback in 1980, reigning somewhat imperiously over a fractious India and increasingly retreating to the stratagem of externalizing internal problems by invoking the threat of the "foreign hand." Her toppling of popularly elected governments in the states of Jammu and Kashmir and Sikkim and her abortive attempt to do the same in Andhra Pradesh had generated a strong backlash, particularly in southern India, and a noisy, nationwide "save democracy" campaign that had promised to unify the fragmented and largely feckless opposition for the first time.

Moreover, there appeared to be no campaign issue on the horizon that would spark the interest of the voters one way or another, as there was with the war in East Pakistan for the 1971 election, the "emergency" rule that backfired and tipped the electoral scales against her in the 1977 election and the bungling of the Janata government that returned her to power in the 1980 election.

Indeed, the Congress (I) Party's position before the assassination, while not so precarious that defeat was a realistic prospect, was shaky enough for want of a focus that both Gandhis were considering running for seats in Parliament from two constituencies each -- the prime minister from her traditional district of Rae Bareli, in Uttar Pradesh, and another, unspecified "safe" district, and her son from Amethi, also in Uttar Pradesh, and a second "safe" district.

Such a precaution seems unnecessary now, given the groundswell of sympathy rising for Rajiv Gandhi and the nostalgia for the family dynasty that his grandfather, Jawaharlal Nehru, began when he became India's first prime minister in 1947.

Capitalizing on that sympathy, the Congress (I) strategists already have started a campaign apparently designed to associate Rajiv with the greatness of his forebears and, at the same time, keep the emotional pitch of voters at a high level.

The party has drafted an official three-line Hindi campaign slogan that translates, "In memory of Indira, support Rajiv, put your mark on the hand." The Congress (I) Party's ballot symbol is a hand facing palm outward.

When urns containing the ashes of the slain prime minister were flown to the capitals of India's 22 states and nine union territories, a special vessel containing -- according to Hindu tradition -- the most important portion of the remains was taken by Rajiv Gandhi in a special train not only to his mother's birthplace in Allahabad, but to Amethi, the election district that was arbitrarily picked by his late brother, Sanjay, and later by Rajiv, as a constituency from which to run for a seat in Parliament.

Every day, Indian newspapers carry numerous full-page advertisements purchased by businesses and government institutions mourning the death of Indira Gandhi and hailing the succession of her son to the premiership. Prime time on the state-owned television has been dominated by reminiscences of Gandhi's 16 years as India's leader, usually followed by commentators' appeals for public support of her son.

For the first time since the apex of her popularity after India defeated Pakistan and created independent Bangladesh in 1971, Gandhi has been referred to by some of the television commentators as Durga, the mother goddess of Hindu mythology who symbolizes strength and victory.

Political analysts who have studied reactions in the aftermath of assassination say that Gandhi will benefit from the sympathy factor most in the vote-heavy Hindi heartland that stretches across northern India from Rajasthan to Bihar, and least in the southern, eastern and western states where linguistic and regional sentiments run strong and where the Congress (I) Party would face uphill battles anyway.

With only 2 percent of India's 740 million population, the Sikhs, who were embittered with the Gandhis over the Army assault on Amritsar's Golden Temple even before the firestorm of anti-Sikh violence by Hindu mobs last week, could not be expected to be a significant vote factor in the election. It is the Hindus in densely populated states like Uttar Pradesh and Bihar who will weigh heavily in the outcome, according to the analysts.

Another factor that Gandhi has working for him, political observers say, is that his mother's assassination and the 1980 death of her son Sanjay in a stunt-plane accident have effectively cleansed the Congress (I) Party of the stigma associated with the 1975-77 "emergency" era in which most civil rights were suspended and thousands of political opponents jailed.

Rajiv Gandhi, who was working as a pilot for Indian Airlines when the draconian emergency measures were imposed, has never been associated with that era. On the contrary, his moderate political outlook and his campaigns against corruption in government had earned him the sobriquet of "Mr. Clean." The opposition parties will also find little comfort in the fact that the issue of Indira Gandhi's alleged dictatorial rule of her party has been removed by her death and that her son is perceived by many as having worked hard in his three years in politics at reviving grass-roots morale in the party, particularly in its youth wing.

The only issues that seem available to the opposition parties are those of the dynastic succession and the government's security lapses in protecting the prime minister and curtailing postassassination violence that left at least 1,000 Sikhs dead. Opposition leaders have sought to exploit both issues, but neither has captured the imagination of the public.

Gandhi has already partly defused these issues by ordering a complete shake-up of the Delhi police command.

The Congress (I) Party working committee is scheduled to meet Monday to elect Gandhi party president shortly before he is expected to go on nationwide television to pledge himself to continue the policies of his mother in what will amount to a campaign keynote speech.

After making that important, tone-setting speech, Gandhi's immediate task will be to consolidate his inherited power, expand his narrow constituent base and fend off the possible rise of regional party bosses who may sense weak leadership at the center.

However the major challenge now facing the 40-year-old prime minister is twofold: to demonstrate that he has the capacity to attract votes for the Congress (I) Party, and to prove by deed rather than by word that he has the strength and leadership qualities necessary to govern a vast and diverse country.