NEW DELHI (Reuters) - Gains by India’s ruling party in a southern state election next month will fall short of a majority, an opinion poll showed, potentially forcing it to seek an alliance to end the rule of the main opposition Congress party in its last big state.

FILE PHOTO: India's Prime Minister Narendra Modi addresses an election campaign rally ahead of the Karnataka state assembly elections in Bengaluru, India, February 4, 2018. REUTERS/Abhishek N. Chinnappa/File photo

A win in Karnataka, the first of three key states to vote this year ahead of a 2019 general election, would give Prime Minister Narendra Modi’s party a foothold in the prosperous south and bolster his chances of a second term.

Modi’s Bharatiya Janata Party could more than double its tally to 89 seats in the 224-seat assembly in May’s state election, but fall two seats short of the Congress tally, according to the opinion poll by television station Times Now and VotersMood Research aired late on Monday.

Regional party Janata Dal (Secular), together with smaller ally the Bahujan Samaj Party (BSP), is likely to win 40 seats and emerge as the kingmaker in an assembly that needs 113 seats for a majority, the poll showed.

Another opinion poll conducted for the India Today news channel this month also predicted that both the Congress and BJP, on their own, would fall short of a majority.

The Janata Dal is confident of forming its own government with the BSP and would not support the BJP or Congress, its spokesman, Ramesh Babu, said.

He denied that the party had a “secret pact” with the BJP, as some Congress leaders in the state have suggested.

Top BJP and Congress leaders have campaigned extensively ahead of the election in Karnataka, whose capital, Bengaluru is known as the country’s information technology hub but has struggled to cope with pressure on its infrastructure.

Election results will be declared on May 15.

“Karnataka is significant for the BJP because it needs to outperform in the south and the east of the country to make up for expected losses in the north,” said Amitabh Dubey, a political analyst with consultancy TS Lombard.

“In the general election they are unlikely to repeat the same result as the last time in states such as Rajasthan and Gujarat.”

Karnataka is the only south Indian state that the Hindu-nationalist BJP has ruled for a full five-year term on its own, following a surprise victory in 2008.

Elsewhere, however, the BJP has been riding high on Modi’s popularity, despite concerns about a lack of jobs. The party or its partners now rule 21 of India’s 29 states, up from just seven when Modi took office in 2014.