"For us, our farmers' welfare is supreme," Modi said at an event in New Delhi.
"India will never compromise on the wellbeing of its farmers, dairy (sector) and fishermen. And I know personally I will have to pay a heavy price for it."
Trump announced an additional 25 per cent tariff on Indian goods on Wednesday, raising the total duty to 50 per cent - among the highest imposed on any US trading partner.
The new tariff, effective from August 28, is meant to penalise India for continuing to buy Russian oil, Trump said.
While Modi did not explicitly mention the US or the collapsed trade talks, his comments marked a clear defence of India's position.
Trade talks between India and the United States broke down after five rounds of negotiations over disagreement on opening India's vast farm and dairy sectors and stopping Russian oil purchases.
India's foreign ministry has called the US decision "extremely unfortunate" and said it would "take all necessary steps to protect its national interests."
The US has yet to impose similar tariffs for China, the biggest buyer of Russian oil. Experts say China's dominance in rare earth minerals - critical to high-tech industries - gives it leverage that India currently lacks.
"The US tariff hike lacks logic," Dammu Ravi, secretary of economic relations in India's foreign ministry, told reporters.
"This is a temporary aberration, a temporary problem that the country will face, but in course of time, we are confident that the world will find solutions."
India is already signalling it may seek to rebalance its global partnerships. Modi is preparing for his first visit to China in over seven years, suggesting a potential diplomatic realignment amid growing tensions with Washington.
Brazilian President Luiz Inacio Lula da Silva said he would initiate a conversation among the BRICS group of developing nations about how to tackle Trump's tariffs.
He said he planned to call Modi and China's Xi Jinping. The BRICS group also includes Russia and South Africa.
India's Ravi added "like-minded countries will look for co-operation and economic engagement that will be mutually beneficial to all sides."
Both supporters of Modi and the opposition Congress party have called on him to respond firmly to the US tariffs, urging action "with self-respect and dignity."
"India's national interest is supreme. Any nation that arbitrarily penalises India for its time-tested policy of strategic autonomy, rooted in the ideology of non-alignment, does not understand the steel frame India is made of," Congress party president Mallikarjun Kharge said.
