The Spanish champions confirmed they had finally made a 'serious offer' - expected to be around £30million - after days of informal talks with the Gunners.
Arsenal have declined to comment and will drive a hard bargain for a player they do not want to leave.
Ready to move? Cesc Fabregas scores for Arsenal against Barcelona last season
But Barca technical secretary Txiki Begiristain and director of football Raul Sanllehi will now lead negotiations with their English counterparts.
Director general Joan Oliver said: 'Everyone knows that Cesc wants toplay for this club and everyone knows that we also want this. But thereis a third major player, which is Arsenal.
'Any deal must go through them and June 1 was the beginning of the period of official negotiations.
'Until earlier there were informal conversations, but since yesterdaythese are formal - and the usual mechanism is to present a formal and concrete offer.
'So yesterday afternoon, we submitted a written bid to Arsenal.'
Fabregas set the ball in motion for a move on May 13 when admitting at a promotional event that he would like to return to the club where he came through the youth ranks before being spirited away to Arsenal in 2003.
Deadline: Fabregas wants closure before the World Cup begins on June 11
Informal talks and very public posturing have taken place since, with a number of Barca keeping up the pressure by talking of their desire to team up with the 23-year-old.
And while Arsenal have kept their counsel, Barca powerbrokers such as Oliver and outgoing president Joan Laporta have given virtually a daily commentary on their plans.
Oliver's announcement that talks had gone to the next step was followed by the club's vVice-president Rafael Yuste, who added: 'I'm hopeful he can sign for the club as soon as possible.
'I'm optimistic and it is clear that he, his family, the players and the entire environment would give a very warm welcome.
Pact: Begiristain (left) will lead negotiations on a deal backed by (from left) Laporta, legend Johan Cruyff and coach Pep Guardiola
'So we will not do anything to thwart his signing. We will not be in any kind of hurry, but we will not pause either.
'Now the ball is in Arsenal's court and, as we have an exceptional relationship with them, I am optimistic.'
Fabregas is under contract at the Emirates Stadium till 2015 and will seek a hefty fee if they cannot convince their captain to stay.
It is understood the Gunners are prepared to argue their star should have a value similar to the world-record £80m deal that took Cristiano Ronaldo from Manchester United to Real Madrid 12 months ago.
Makeweight: Chygrynskiy could be offered on loan to Arsenal as a sweetener
Barca's initial £30m value is provocatively low, but Laporta has admitted in recent days that there is room for compromise.
He will step down as president at the end of the month, but none of those vying for his job would stand in the way of signing Fabregas, least of all the frontrunner Sandro Rosell.
Barca will look to reduce their cash outlay on the deal by offering players in part exchange.
There are many options, but few that interest Gunners boss Arsene Wenger.
Ukraine defender Dmytro Chygrynskiy, who struggled at the Nou Camp following a move from Shakhtar Donetsk last summer, is the latest mooted as a possible makeweight in the deal.
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