The International Atomic Energy Agency (IAEA) board is due to hold an emergency session in Vienna on Thursday to consider sending Iran to the UN Security Council for sanctions over its nuclear programme.
David Mulford, the US ambassador to India, said last week that if India did not oppose Tehran at the IAEA, a landmark India-US nuclear co-operation pact could be in trouble.
A senior official said: "We cannot vote with the US after his comments. We're planning to abstain."
Although Mulford later said he had been quoted out of context and expressed regret, his remarks triggered a domestic furore with allies in the ruling coalition of Manmohan Singh, the prime minister, and opposition groups accusing the government of selling out to Washington.
The official, who spoke on condition of anonymity, said: "We are still hoping the crisis won't go to a vote and Iran will get some more time to resolve it through talks.
"But if it does, then Ambassador Mulford has made it easy for us."
The official said India backed a Russian compromise plan under which Moscow would enrich Iranian uranium fuel, a proposal backed by China.
Reluctance from veto-wielding Security Council members Russia and China over imposing economic sanctions on Iran threaten to undermine US and European plans for tough action against Tehran.
India and Iran have historically been on good terms.
But New Delhi surprised the world in September by supporting Washington at an IAEA vote that declared Iran had failed to comply with its international obligations.
An Indian foreign ministry official said India's abstention now could slow the closing of a civilian nuclear co-operation deal with the US under which Washington has promised to help New Delhi boost its atomic programme to meet its growing energy needs.
"We know that this could create problems in the US Congress, but we don't seem to have many options now," the official said. "We will explain our compulsions to our interlocutors."
India hopes to sign a nuclear
co-operation deal with the US
The India-US atomic deal seeks to reverse a nearly 30-year-old ban on nuclear co-operation with New Delhi, which has tested nuclear weapons, and needs the approval of US Congress.
Both sides have been confident about clinching it before a visit to India by George Bush, the US president, in March although details of the accord are still to be negotiated, including crucially a plan to separate India's civil and military nuclear facilities.
Singh, who also holds the portfolio of foreign minister, said his government would not be pressured into doing anything that hurt national interests.
"We will do what is right for our country. India's national interest is our prime concern. Whether it is domestic or international policy, we will not act under pressure on anything," the Hindu newspaper quoted Singh as telling reporters when asked about the Iran vote.