Regional parties in southern India will be put to the acid test in parliamentary elections this month in a crucial showdown with the Congress (I) Party government of Prime Minister Rajiv Gandhi.

From all outward appearances, national-regional relations and the Congress Party's gradual concentration of power in New Delhi will dominate the campaign for the Nov. 24-28 elections in the southern states, where sympathy for Rajiv Gandhi following the assassination of prime minister Indira Gandhi has been less than in the Hindi-speaking northern states.

Interviews with party leaders and campaign strategists on both sides in the southern contests indicate that the movement for regional assertiveness that gained momentum during Indira Gandhi's last years in power is at a crossroads and that the Congress (I) Party has been presented with an opportunity to recover some of its losses in southern India.

Rajiv Gandhi is splitting his first week of road campaigning between the vote-heavy northern state of Uttar Pradesh and the southern states of Andhra Pradesh and Karnataka.

Gandhi launched his electoral campaign Saturday, drawing large and enthusiastic crowds in the northern state of Uttar Pradesh, Reuter reported. Tight security surrounded a crowded sports stadium in the city of Bulandshahr, where 50,000 people gathered to hear Gandhi deliver his first campaign speech.

With 220 of the 542 elective seats in the Lok Sabha, the governing house of Parliament, the five populous states in northern India's "Hindi Belt" -- Uttar Pradesh, Bihar, Madhya Pradesh, Haryana and Rajasthan -- have been the power base of every prime minister since India won independence in 1947.

But ruling parties also have traditionally relied on southern India to provide swing votes necessary for a parliamentary majority, and political analysts here and in New Delhi say that the Congress (I) Party desperately needs at least one of the large southern states to ensure an electoral victory.

Before Indira Gandhi's assassination Oct. 31, Congress (I) appeared headed for deep trouble in the southern states. Because she reacted to growing regional assertiveness by tightening controls on the southern states and virtually equating regional sentiments with sedition, her popularity had begun to wane in southern India, with voters appearing to turn increasingly to parochial alternatives.

An attempt to topple the popularly elected opposition government of former matinee idol N.T. Rama Rao backfired and resulted in a strong anti-Congress backlash in the state of Andhra Pradesh.

The reaction spilled over to neighboring Karnataka State, where it was widely feared that Congress (I) would attempt to overthrow the Janata Party coalition government of Chief Minister Ramakrishna Hegde, a populist politician with wide appeal here.

In Tamil Nadu, the serious illness of M.G. Ramachandran, a former film star and now chief minister, threatened to unravel the ruling alliance of the Congress Party and Ramachandran's All-India Anna Dravida Munnetra Kazhagam Party, possibly denying the Congress (I) its share of 20 of the state's 39 parliamentary seats. Some political observers here say that without Ramachandran's popular following, the coalition would collapse. Others say a groundswell of sympathy for the ailing film star-turned politician, who is in a New York hospital for treatment of a kidney ailment and stroke, could help Gandhi.

The Congress (I) Party's waning fortunes in the south were accompanied by an unusual coalescing of the normally fractious opposition parties, which as recently as September had led some party strategists to question whether Congress (I) could gain a working majority in Parliament, much less retain the two-thirds edge it won in the 1980 election.

Now, however, opposition unity appears to be disintegrating, enhancing the Congress (I) Party's chances to pick up the needed swing votes in the south.

Squabbling between opposition parties has thrown into disarray the complicated Indian practice of "seat adjusting," in which the opposition parties make deals to run a single candidate against the Congress Party in selected parliamentary districts.

Hegde, the chief minister of Karnataka and state Janata Party leader, said in an interview, "It is very unfortunate that the opposition couldn't come to an agreement on seat adjustments, but that's the way of Indian politics. When the time comes to vote, the people will vote for the party they like. They've always voted so far for a strong central government, but this time it is going to be different. In this election, people might vote in a coalition government."

Hegde said that any advantage that Rajiv Gandhi gained from sympathy generated by his mother's assassination will be dissipated in southern India by election day, and that the opposition will gain ground on the issues of concentration of power in New Delhi, corruption in the Congress (I) Party, and government mishandling of sectarian tension in strife-torn Punjab and Assam states.

Hegde said Congress (I) has an advantage among the most impoverished rural voters and "scheduled castes," or low castes, because "she Indira Gandhi left an indelible imprint on them. For them, it doesn't matter whether she is alive or not. They think she will continue in one form or another."

But he said he believes a majority of voters in southern India will vote against the Congress Party's concentration of power in New Delhi. He predicted that his Janata Party, which swept into power in the state assembly elections last year but which is outnumbered 27 to 1 by the Congress (I) Party in the national Parliament, will win a majority of parliamentary seats this month.

The state's Congress (I) Party campaign manager, former chief minister S. Gundu Rao, had a different perspective, predicting that his party would retain 27 of the 28 Karnataka seats in Parliament because "people here were very attached to Madam Gandhi. Sympathy for her will go a long way."

However, he conceded that the clumsy Congress (I) attempt to topple Rama Rao in Andhra Pradesh -- a move widely believed to have been initiated by Rajiv Gandhi when he was the party's general secretary -- had "damaged" Congress (I) in that state, and that the opposition would win as many as 32 of the 42 parliamentary seats there.

Gundu Rao said that Rajiv Gandhi and the new Congress Party leadership had made a major effort to draft new candidates in the region with "clean images" and progressive outlooks. Paralleling that effort, Congress (I) also has dropped several prominent candidates who have been associated with corruption.