Ferguson, speaking for the first time since the media blackout that followed Sunday's 3-1 defeat to Liverpool, said Arsene Wenger's side had rejuvenated the rivalry that existed between the two sides when they were routinely considered the only plausible champions.
The Scot said: "Clearly they (Arsenal) represent the main danger to us achieving our ambitions in a revival of the rivalry of a few years ago, and I am sure they regard us as the major threat to their hopes."
Following their Anfield reverse, the Red Devils are now just three points clear at the summit of the Barclays Premier League having played one game fewer.
The sides also meet in the FA Cup quarter-finals on Saturday, prompting Ferguson into an assessment of the Gunners' form.
Ferguson said: "Last season they (Arsenal) faded around the February to March period to leave Chelsea and ourselves in a two-horse race that saw us pipped at the post by a point.
"I think most pundits expected to see something similar this season, plus a challenge from Spurs and Manchester City to make it even more difficult for Arsenal to get back up to the top.
"But Arsene Wenger and his players have rearranged the pecking order somewhat to come storming through to lie in second place."
As for the Liverpool match, Ferguson held his hands up and admitted United deserved to lose to their rivals.
He added: "I have no excuses for the poor performance at Liverpool, who were the better team and deserved their win. I was disappointed because we didn't perform to the level I expect and which, to be fair, we generally achieve."
Source: PA
Source: PA