Congress, which has struggled to implement planned reforms since it held onto power in the 2009 general election, campaigned hard in a state that is seen as a key pointer towards the next national poll due by 2014.
Several voter surveys put the Congress party, which leads a fractious coalition in New Delhi, in fourth position after the staggered elections in the northern state of Uttar Pradesh ended on Saturday.
Congress was expected to increase its strength in the 403-seat state assembly from 22 to about 50, but party organisers had hoped for a far more significant increase.
Rahul Gandhi, the scion of the Nehru-Gandhi dynasty that has dominated post-independence Indian politics, spent weeks on the campaign trail in a display widely seen as a test of his prime ministerial potential.
“We all know that exit polls have gone wrong in the past, and this will happen now again,” Congress general secretary Digvijay Singh told the Press Trust of India in response to the surveys.
He said the party would win at least 100 seats.
The official election results, to be released on Tuesday, were also predicted to deliver bad news for Uttar Pradesh’s firebrand Chief Minister Mayawati and her Bahujan Samaj Party.
Mayawati, who uses only one name, is tipped to lose office as the rival Samajwadi Party makes strong gains in Uttar Pradesh, a deeply impoverished state of 200 million people.