"It is essential that there be this institution," Pawar, whose party in a key ally of Congress, told reporters here.
Pawar's statement came in the backdrop of Congress deciding to write to Speaker Sumitra Mahajan to seek an immediate decision in the matter and Congress president Sonia Gandhi insisting that being the single-largest party and pre-poll alliance it was entitled to the post.
"We are the single-largest party. We have got a pre-poll alliance. Hence, we are entitled to the Leader of Opposition's post," Gandhi had said on Monday, breaking her silence on the issue.
About the upcoming assembly elections in Maharashtra, due in October, Pawar said a decision on the number of seats to be contested by Congress and NCP would be taken at the national level.
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Asked if NCP contesting 50 per cent (144 of state's 288) seats would be a precondition when leaders of the two parties sit to discuss seat-sharing, Pawar said, "it can be more than 144 or less than 144. Winnability will be a factor in the talks."
Asked if NCP will project any leader as a CM candidate ahead of polls, Pawar said, "we will first see what the picture is from the other side. Then we will decide."
When his attention was drawn to Chief Minister Prithviraj Chavan pleading ignorance about the reported offer from Congress leadership that Pawar lead the joint poll campaign in the state, the NCP chief said, "Chavan was not present at the meeting when the proposal was made.