The PM has said he will give MPs more time to debate his Brexit deal, if they agree to a 12 December election.
Boris Johnson told the BBC he expected the EU to grant an extension to his 31 October deadline, even though he "really" did not want one.
But Jeremy Corbyn said he would not support an election until a no-deal Brexit is "off the table".
EU leaders could give their verdict on delaying Brexit for up to three months on Friday.
Commons leader Jacob Rees-Mogg told MPs the government would on Monday table a motion calling for a general election.
Under the 2011 Fixed-Term Parliament Act, two-thirds of MPs must vote for a general election before one can be held.
In a letter to Labour leader Mr Corbyn, Mr Johnson said his "preferred option" was a short Brexit postponement "say to 15 or 30 November".
But Mr Corbyn said: "Take no-deal off the table and we absolutely support a general election.
"I've been calling for an election ever since the last one because this country needs one to deal with all the social injustice issues - but no-deal must be taken off the table.
"The EU will decide whether there is an extension tomorrow... and then we can decide."
Mr Johnson wrote that, in that case, he would try to get his deal through Parliament again, with Labour's support.
The prime minister added that he "assumes" Mr Corbyn "will cooperate with me to get our new Brexit deal ratified, so we leave with a new deal rather than no deal".
If, as widely expected, the EU's Brexit delay is to the end of January, Mr Johnson said he will hold a Commons vote next week on a 12 December election.
If Labour agrees to this, the government said it will try to get its deal through before Parliament is dissolved for the campaign on 6 November.
Treasury sources told the BBC that the Budget would not now be delivered on 6 November as scheduled.
Where parties stand on election
- Conservatives - Boris Johnson has requested an election twice already - but not all of his MPs are on board with the idea, arguing that the focus should be on delivering Brexit first
- Labour - Has insisted it wants an election but won't vote for one until a no-deal Brexit has been firmly taken off the table. Some of its MPs from Leave voting areas may take a different view
- SNP - The party's leader at Westminster, Ian Blackford, said "we want an election but these terms are not acceptable," adding that the poll should take place earlier than the middle of December
- Lib Dems - Would prefer another referendum but have said they would vote for an election if there was a long enough extension. Leader Jo Swinson said she wanted to see what the EU said on Friday before deciding
- DUP - Sammy Wilson, the party's Brexit spokesman, has indicated that the unionists could support an election in a bid to secure better terms with the EU
- Independent Group for Change - Leader Anna Soubry said an election "wouldn't solve anything" and called again for another referendum
- Plaid Cymru - The party's four MPs are likely to vote against an election, with the party arguing for another referendum instead
- Green Party - The party's sole MP, Caroline Lucas, looks set to vote against an election, saying in a tweet the UK could still "crash out" with no-deal if MPs can't amend the Withdrawal Agreement
The prime minister told BBC political editor Laura Kuenssberg: "I'm afraid it looks as though our EU friends are going to respond to Parliament's request by having an extension, which I really don't want at all.
"So, the way to get this done, the way to get Brexit done, is, I think, to be reasonable with Parliament and say if they genuinely want more time to study this excellent deal, they can have it but they have to agree to a general election on 12 December."
Asked what he would do if Labour refused to vote for an election, he said: "We would campaign day after day for the people of this country to be released from subjection to a Parliament that has outlived its usefulness."
The prime minister has repeatedly insisted the UK will leave the EU on 31 October, with or without a deal.
But he was forced to send a letter to the EU requesting an extension, under legislation passed by MPs last month.
MPs voted on Tuesday to back the first stage of the Withdrawal Agreement Bill, putting the deal the PM agreed with Brussels into law - but rejected Mr Johnson's plan to push it through the Commons in three days.
The BBC's Europe editor Katya Adler says EU leaders are set to decide on Friday whether to grant the UK a three-month Brexit extension - although the decision could be delayed to Monday.
Most EU nations back it but France "is digging its heels in", she adds.
So there could be an emergency summit in Brussels on Monday to allow leaders to reach agreement face-to-face.
Boris Johnson cannot be remotely sure Labour and the smaller parties will let him have his way. The SNP and the Lib Dems are both tempted to go for an election as soon as a three month delay is agreed.
The Labour Party's official position has always been that they would agree to an election, in fact officially they are chomping at the bit, like the other parties, as long as a delay is agreed.
One senior member of the shadow cabinet predicted they would not be able to withstand the pressure if the Lib Dems and the SNP said yes.
Jeremy Corbyn himself, and certainly one group in his camp, are understood to be very tempted too. But, just as in 2017, lots of Labour MPs are horrified at the idea, partly because of Labour's standing in the polls.
But also, there are senior shadow cabinet ministers who believe the smart thing would be to leave the PM in his purgatory, twisting, unable to get his bill through, unable to get to an election.
In short, the position is fluid, and Labour is having words with itself tonight.