The ruling party of Prime Minister Narendra Modi has tightened its grip over India’s populous northern belt, results of state elections showed Sunday, expanding its dominance of a key region ahead of general elections in which Mr. Modi is seeking a third term.

The results of voting for the governments of four states, with a cumulative population of more than 240 million people, was another blow to the dwindling fortunes of the main opposition party, the Indian National Congress. The party, which ruled for a majority of India’s history as a republic, has struggled to claw its way back after Mr. Modi rose to national power in 2014.

The Congress party was hoping to use the state elections to build momentum for national elections next spring, but instead lost all three states in which it was pitted against Mr. Modi’s Bharatiya Janata Party, or B.J.P.

The B.J.P. managed to re-elect its government in Madhya Pradesh, with a bigger margin, and topple Congress in Chhattisgarh and Rajasthan. The only victory for Congress came against a smaller regional party in Telangana, in India’s south, where Mr. Modi’s Hindu nationalist politics has faced resistance. The results of elections in a smaller fifth state, Mizoram, are expected on Monday, but the race there is between two smaller regional parties.

“When the Congress goes up against the formidable organizational and electoral machinery of the B.J.P., burnished by Prime Minister Modi’s charisma, it collapses,” Arati Jerath, a New Delhi-based political analyst, said about the opposition’s performance in the north. “This is the B.J.P.’s big advantage in 2024.”

While Indian elections trends could easily fluctuate in coming months, Ms. Jerath said the B.J.P.’s further consolidation of its support base, where its Hindu nationalist politics have taken strong root, puts it in a comfortable position ahead of the elections in the spring.

Mr. Modi already has a big plan for further galvanizing his base of support: the inauguration in January of a massive Hindu temple in Ayodhya, in the northern state of Uttar Pradesh, that is being constructed on the site of a destroyed mosque. Demands for the construction of the temple helped turn Hindu nationalism into a major political movement in the 1990s and make the B.J.P. a national power.

The state elections this month, while usually not a direct indication of how people vote in the general elections, were important in their timing. For the Congress party, it was seen as chance to show that it was getting its house in order, and regaining a winning touch.

In the months before the elections, the Congress had scored a victory against the B.J.P. by winning the southern state of Karnataka, the cash-rich hub of the Indian tech industry. It also formed a national alliance, called INDIA, that included smaller and regional parties — an indication of its acceptance of an evident truth: that Congress cannot win a fight alone against Mr. Modi’s formidable B.J.P. and its considerable resources.

Going into the state elections this month, however, the Congress decided to fight alone in states where it saw a good chance of victory against the B.J.P.

The refusal of Congress to join together in these elections with the same parties it hopes to ally with in the national fight against Mr. Modi will diminish its standing in the eyes of those partners, analysts said.

“It is going to be very difficult for them to put up a credible challenge against the B.J.P. in 2024,” said Rahul Verma, a fellow at the Center for Policy Research in New Delhi. “Now I am not sure how the INDIA alliance is going to pan out.”

In the three states where the B.J.P. and Congress went head to head, there was little to differentiate the parties, with both mainly focusing on handouts — from subsidized gas cylinders, to deposits for farmers and married women, to payments for books and school bags for students. Both parties faced voter fatigue, allegations of corruption and infighting in their state ranks.

But to cover for its weakness, the B.J.P. had what the Congress has struggled to find, analysts said: ideological clarity and charismatic national leadership.

The B.J.P stands clearly for Hindu nationalism and its divisive vision for turning India into a Hindu-first state. Mr. Modi, projecting himself as an ambitious champion of development as well as Hindu interests, also has a strong pull with voters across the country. His government has used the resources of the top-heavy and unequal Indian economy for well-targeted welfare schemes, handed out often in his name. In states where local B.J.P. leaders were struggling in the elections, it was Mr. Modi’s face on the posters; the handouts for voters were presented as “Modi’s guarantee.”

In comparison, the Congress has struggled to present a leadership that can put up a fight against Mr. Modi, or a clear vision for its secular ideology. Mr. Modi’s effort to harness grassroots Hindu networks over the past decade and his firm grip over the national media have significantly shifted India’s secular mainstream, particularly in the country’s north.

Rahul Gandhi, the Congress leader who would likely be its candidate for prime minister if the party wins in the spring, is often caricatured by Mr. Modi and his aides as entitled and a lightweight.

While Mr. Gandhi has presented the Congress as standing for harmony and secularism against the divisive Hindu-first politics of Mr. Modi, that difference has not been projected clearly by officials at the state level.

In the elections this month, Madhya Pradesh, with a population of more than 80 million, and which the B.J.P. had ruled for most of the past two decades, was seen as a major test of whether the Congress could use the B.J.P.’s weaknesses to score a victory.

The B.J.P. government of the state had been accused by critics of widespread corruption, political infighting and causing communal tensions and riots with its Hindu-first policies.

The Congress also accused the B.J.P. of using underhanded methods when in 2020 it toppled the Congress government that had come to power two years earlier with the help of smaller parties. The B.J.P. managed to take power that year by getting a number of Congress deputies to change sides.

Despite the criticism, the B.J.P. still held on to Madhya Pradesh — and won about 50 more seats, according to the results on Sunday.

“As a political party, as an organization, the B.J.P are much more agile and adaptive,” said Mr. Verma, the analyst. “They are ready to take bold moves, to experiment for winning at any cost.”