Millions of voters in India go to the polls Thursday in the world's largest free election, and former prime minister Indira Gandhi -- who suffered a humiliating defeat nearly three years ago -- is an overwhelming favorite to recapture the leadership of this country.

The big question is whether Gandhi's Congress I (for Indira) Party will gain enough seats in Parliament to form the government itself or whether she will have to forge coalitions with other parties.

In either case, she is considered the most likely person to become India's next chief of government.

Balloting starts Thursday for an estimated 144 million voters in 226 election districts. The rest of the country's 362 million voters go to the polls Sunday, with the first results not due until after the polls close Sunday night.

It is unlikely, though, that the winning party will be known until Monday and if the election is close, it could be impossible to be sure who the new prime minister will be until Tuesday or Wednesday.

The Indian electorate is so large that it takes two days to complete the polling. Thursday's ballots are locked up in district strongrooms, guarded by police and representatives of the competing parties, who place their own locks on the ballot boxes along with the official ones.

No major issues have been developed during the unusually long, five-month campaign, which largely became a battle of personalities and appeals to voters made along caste and religious lines.

Gandhi insisted she could run the country better, while her opponents contended she would return to the excesses of her 20-month emergency rule, in which tens of thousands of Indians were jailed and strict censorship was clamped on newspapers and magazines. Some have even said this could be India's last free election if Gandhi wins.

"It is a contest between fear of Mrs. Gandhi's return and contempt for the politicians who succeeded her," said one Indian government official who asked that he not be named.

It appears that contempt is winning over fear. A poll published in the latest issue of the magazine India Today gives the 62-year-old Gandhi 291 seats in Parliament -- enough for her to form a government with no help from any other party.

Most of the forecasters, however, do not believe she will win that big a majority, although few doubt that her party will pick up the largest block of seats in the 542-member Parliament.

Gandhi's closest competitor is the five-party Janata coalition that defeated her in March 1977 over the issue of her emergency rule. This time the Janata is headed by 71-year-old Jagjivan Ram, leader of India's 100 million untouchables and a venerable politician who has been a member of every Indian Cabinet save two since this country gained independence from Britain in 1947.

Charan Singh, 77, the caretaker prime minister, is rated a poor third. His Lok Dal party, a breakaway from the Janata, has based its campaign on an appeal to a very narrow group -- the small landholder farmers of which Singh is a leading member. He may be the spoiler for Ram, however, taking away votes from the Janata in the northern Indian states where both are strongest.

The personal fate of two of the three top contenders for prime minister -- Gandhi and Charan Singh -- will be known early as they are running from districts that go to the polls Thursday.

The election campaign has been going on since August, when the Janata government of Morarji Desai fell and neither he nor Charan Singh could get enough votes to form a new government. India's president, N. Sanjiva Reddy, declined to give Ram a chance, named Singh as caretaker prime minister and called for new elections.

Despite the long campaign, the election has not generated much enthusiasm among voters. One longtime Indian political observer said voters regard the current campaign with "apathy and contempt for most of the politicians who are running."

The main question is whether or not Gandhi -- who is often called "the empress of India" or "India's iron lady" -- will be returned to power.

"If Mrs. Gandhi does win the election," said India Today in its Tuesday issue, "It will be a victory of stamina, shrewd manipulation, charisma and effective organization over a flatfooted, effete, blundering opposition . . .

"Her successors [after the 1977 election] by their criminal ineptitude in government have virtually presented the country to her on a silver platter."

Since Desai's government took power, India has faced increased violence both between Hindus and Moslems and between different castes. In addition, inflation has climbed 20 percent in the past year, shortages are common for such household necessities as kerosene for cooking, sugar and, in some places, salt. Disruptions of electric power and diesel fuel supplies have occurred and there have been both police strikes and widespread labor unrest.

Gandhi has attempted to capitalize on issues of crimes and inflation. One U.S.-style newspaper advertisement focused on the increase in the price of onions, a staple in Indian cooking, while another complained about crime in the streets.

The Janata has tried to counter by saying things are not as bad as she makes it appear. But for Charan Singh's party, Gandhi is the issue. He has said Gandhi plans to whip her opponents the way they do in Pakistan.

A side issue is Gandhi's 33-year-old son, Sanjay, who has been blamed forr pushing many of the excesses of the emergency, including vast numbers of forced sterilizations.

He has also been accused in an official government report of using his mother's position to gain special privileges for a project to build a car that never reached the assembly line. In the process, though, he has been charged with enriching himself and his friends. He also has been convicted of crimes stemming from the emergency rule.

Sanjay Gandhi, though, appears likely to win election from the same district where he was defeated in 1977 by 76,000 votes.

Indira Gandhi is running from two districts, but the most important is the Uttar Pradesh constituency of Rae Bareli, where she personally was defeated by 55,000 votes in 1977.

This time, however, she is a heavy favorite to defeat her main opponent, former princess Vijaya Raje Scindia, whom Gandhi jailed during the emercency. The man who defeated her in 1977, Lok Dal President Raj Narain, is not even running for reelection.

The candidates are appealing to castes and religions as they never have in India's past six elections.

Gandhi traditionally has won the vote of the untouchables, but this time Ram is expected to split it with her. Although he is an untouchable -- the lowest class in the Hindu caste system -- he never has been a fighter for their rights and many caste members view him as sort of an Uncle Tom.

But caste pride may upset that prediction. Ram is the leading untouchable politician and would be the first member of that caste to be prime minister. Many untouchables were reported upset when Reddy refused to let Ram try to form a government last August.

Untouchables make up about 18 percent of the electorate and they can be an important swing factor in many key constituencies. Gandhi lost the untouchable vote in 1977 after Ram, a senior member of her Cabinet, defected from her Congress Party and joined the Janata.

Defections have played a major role in this campaign from the start, and rumors were strong that even Ram -- the leader of one of the three major parties -- was thinking of jumping to Gandhi's side.

Gandhi did pull a key Moslem politician, H.N. Bahuguna, from Charan Singh's Cabinet, to her side and she assiduously courted Syed Abdullah Bukhari, the imam of Delhi's Jam a Masjid mosque.

Again, Gandhi in the past won most Moslem votes, but they abandoned her in 1977 over the issue of forced sterilization. Despite support from the imam and Moslem politicians such as Bahuguna, some observers believe Moslems -- who make up 15 percent of the voting population -- will have long enough memories to vote against Gandhi this time.