The British rock legend -- who's a HUUUGE soccer fan -- was leaving Catch in L.A. over the weekend when we asked about the biggest football news in the U.K. ... Rooney's DUI arrest in England.
"He's been a great English football [player] and we all make mistakes," Stewart said ... "And he's still a great guy. A great influence on all the youngsters."
Rooney was busted early Friday morning when he was pulled over in a VW Beetle and failed a breathalyzer.
According to reports, the Everton striker's bosses are pissed -- and he could get hit with a $415,000 fine over the incident.