By Rupam Jain

ALLAHABAD, India (Reuters) - Prime Minister Narendra Modi has notched up gains in elections to India's upper house of parliament, and is seeking to drive home the advantage when his nationalist ruling party meets to devise a strategy to win India's biggest state.

Modi drew standing ovations from U.S. lawmakers this week on a visit to Washington D.C. but, like President Barack Obama, has faced a struggle in his two years in power to get legislation through a hostile second chamber.

That job may have become slightly less difficult after his nationalist Bharatiya Janata Party (BJP) and its allies added five seats in Saturday's upper house polls, but with 74 seats in the 245-chamber they remain in a minority.

BJP leaders were due to meet later on Sunday to finalize their strategy to win the 2017 election in Uttar Pradesh, India's most populous state, knowing that defeat would handicap Modi and sap his chances of winning a second term.

"We have to win Uttar Pradesh to change the destiny of India," BJP national secretary Sidharth Nath Singh said to Reuters ahead of the two-day meeting in Allahabad, eastern Uttar Pradesh.

The opposition Congress alliance lost three seats to 71, with regional parties holding the balance of power, according to media tallies. With Congress down but not yet out, Modi will still have to cut deals to pass tax, labor and land reforms.

Modi swept Uttar Pradesh in the 2014 general election, helping him to claim the biggest lower-house majority in three decades. But he is unlikely to repeat that result against tough opposition from regional parties.

A senior BJP official said Modi's closed-door brainstorming session would mobilize grassroots activists to consolidate the majority Hindu vote base and devise a formula to play up Hindu-Muslim polarization and caste politics.

(Editing by Douglas Busvine and Christian Schmollinger)