Third Front, CPI(M) General Secretary Prakash Karat said talks were on with the JD(U) leadership and "we are saying that they have a significant role to play after the elections."
Asked whether JD(U) would risk its government in Bihar by leaving the BJP, he said it was for that party to decide.
"Nitish Kumar has carved out a very strong position in Bihar and independently today he is a major force. So he can strike out, I think .. Take the plunge like (BJD chief) Naveen Patnaik has done. Nitish Kumar will emerge as a major force in Bihar. So he could go ahead without depending on BJP or any other party. I think it will be in his interest," he told Karan Thapar on the 'Devil's Advocate' programme.
On the possibility of a hung Parliament and consequent instability, the CPI(M) leader said that there would not be any instability as a government would be formed and "if we don't get the type of government we want, then we will be in the opposition."
He, however, exuded confidence that Third Front could emerge as "number one" in the elections and said it would be for the Congress to decide whether it would facilitate a secular government at the Centre.
Karat said there would be a "realignment" after the elections and added that parties like JD(U) and NCP would have to decide whether they would join the Left-initiated combination of non-Congress secular parties.
Asserting that the BJP would not be in the picture at all, he said the UPA has started disintegrating and "it is very clear now that nobody can form government without the Third Front's involvement or support."
Asked whether the front would go with BJP or Congress if it did not get the required numbers, he ruled out going with BJP and said "nobody will have the numbers. It will be for Congress to take a decision whether they will facilitate the formation of a secular government at the Centre."
He said "the Third Front is going to do well. If you take into account the BSP, which is now fighting separately but will come with us after elections, (these parties) are doing pretty well. We can match the Congress and BJP easily.
"We may be number one. Don't forget that the UPA has practically ceased to exist. So we are talking about Congress with very few allies. I think the struggle is between Congress and the remaining allies that it has and the non-Congress, non-BJP parties. BJP is not going to be in the reckoning."
The Congress would have to decide what it would do if "they cannot form a government with the numbers that they would have along with its allies" like Trinamool Congress, which he described as "very undependable".
Referring to Congress' statements wooing the Left for support, the CPI(M) General Secretary said "I am telling the Congress that you have to deal with this combination of 10-11 parties".
He also made it clear that the Left would take a decision on the post-poll situation along with its allies BJD, TDP, AIADMK and JD(S) and "not in isolation".
"Whatever decision we take will be with the BJD, TDP, AIADMK and JD(S), all of us together will take a decision."
Asked if they would agree to support a Congress-led government if all these parties wanted, he said "we will go with whatever this combination decides and we are confident that they will remain steadfast in having a non-Congress government at the Centre."
To a question whether Left would support a combination where Congress remains a part but does not join government, Karat said "the situation will be a reverse, that is, Congress will have to consider the prospects of a secular government at the Centre."
On the economic situation in the country, he said the Manmohan Singh government had "underestimated" the adverse impact of the global economic crisis.
Growth would be lower and "more dangerous is the fact that they are underestimating the serious loss of jobs", he said, adding that about 25 lakh jobs have been lost in the last six months.