Most EU states were understood to favour a three-month delay, with an option to end earlier if a deal is ratified sooner than this by the UK Parliament, the BBC reported.
But France has argued for a shorter extension to the October 31 deadline.
The EU's decision on what length of extension to offer, which will be discussed in a closed-door meeting in Brussels on Friday morning, comes after Johnson said that he would give MPs more time to debate his Brexit deal if they backed a December 12 poll.
The UK government has also said that it has planned to bring forward a House of Commons vote on an early general election on October 28 if the EU offers a delay until January 2010, as it was widely expected.
But the chances of enough MPs backing the motion, which under the Fixed-Term Parliaments Act requires the support of two-thirds of MPs, appear uncertain, with opposition Labour Party not committing to how it plans to vote.
On Thursday night, there were reports the party's official position was to abstain on the vote, ending any chance of it gaining enough support.
But in an interview later, Labour leader Jeremy Corbyn said: "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... and then we can decide."
Should enough MPs back an election, they would have until November 6 to debate Johnson's Brexit deal, the BBC quoted the government as saying in an earlier statement.
( With inputs from IANS )