* Milan will walk out of all matches if subjected to racism-Berlusconi
* Boateng says would do it again even in Champions League match
* Authorities accused of not doing enough
* Racism widespread in Italian stadiums
* Town brings civil suit against offending fans (Adds Boateng quotes)
ROME, Jan 4 (Reuters) - Racist chanting that led AC Milan players to walk off the pitch during a friendly match provoked howls of outrage in Italy on Friday, while club owner Silvio Berlusconi vowed his team would abandon all matches where they suffer similar abuse.
Milan's Ghanaian midfielder Kevin-Prince Boateng kicked the ball into the stands, removed his shirt and led his team mates off the pitch 26 minutes into the match on Thursday after monkey chants and jeers from fans of lower division team Pro Patria directed at him, Urby Emanuelson and Sulley Muntari.
Boateng said he would do it again, even in a high profile match.
"I don't care what game it is - a friendly, Italian league or Champions League match - I would walk off again," the German-born 25-year-old told CNN.
"I'm sad and angry that I'm the one that has to take action. All the people who support me would support me in a big game."
Milan's owner backed his player.
"I guarantee that in all matches, including international ones, where incidents of this type occur Milan will leave the field," former Italian Prime Minister Berlusconi said.
The incident revived debate in Italy about whether authorities are doing enough to combat a deep-seated problem.
The mayor of Busto Arsizio, the northern hometown of Pro Patria where the incident occurred, said his administration would sue the fans responsible for the chanting. Local police say they are questioning fans to identify the culprits.
"We have begun a civil claim against the imbecile thugs that have stained the city," mayor Gigi Farioli told Sky Italia television.
"Tomorrow an education drive will be launched, with concrete measures against racism in and out of the stadium," he said, adding that AC Milan and the players involved had been invited to participate. But he said Boateng was "unprofessional" to kick the ball at chanting fans.
Boateng's action was widely applauded, however, and prompted renewed criticism of authorities for not taking stronger action to wipe out the racist insults that are commonplace at Italian grounds.
"Finally, thanks to Boateng, there has been an adequate response to the demented people that chant racist choruses in the stadiums," wrote Pierluigi Battista in an editorial in the respected Corriere della Sera daily.
He called for games to be suspended and points deducted from the team of the offending fans even in Serie A matches as soon as there was racist chanting.
Berlusconi, who is currently running for election, said he admired the team's response to "a disgraceful episode of racism" and said he had telephoned Boateng to congratulate him.
France's former AC and Inter Milan player Patrick Vieira said on Twitter: "Now is the time for the football authorities to stand up and do something. We need to see real actions that will have a genuine influence."
Italian football federation (FIGC) president Giancarlo Abete said he had asked for a meeting with Italy's police chief Antonio Manganelli to discuss closer cooperation and a police presence in stadiums following the incident.
He said authorities "could order the referee to suspend the match" in certain situations.
Late last year 10 fans of London side Tottenham Hotspur, which has a large contingent of Jewish supporters, were injured, one of them gravely, when dozens of anti-semitic "ultras" stormed a central Rome bar in a well-planned attack.
Pro Patria has been fined 15,000 euros ($19,600) over the last year for racist chants, Italian press reported.
Manchester City and Belgium player Vincent Kompany was another of thousands to express their support for Boateng's action on Twitter.
"Act of racism against Boateng during Milan's friendly. How about becoming extremely intolerant towards racist idiots? They need to be told," the defender wrote.
Troubled Manchester City player Mario Balotelli, himself the repeated target of racist chants before he abandoned Italy to go and play in England, praised Boateng's "brilliant work".
The Italian striker, who has endured monkey chants and bananas thrown onto the pitch, last year threatened to walk out of the Euro championship if he heard any racial slurs.
But the Pro Patria chairman, Roberto Centenaro, suggested tackling the problem would be difficult.
"You certainly cannot change the mentality of people who have come to the stadium for 30 years and have these ideas. Clearly we must start with the young," he said. ($1 = 0.7666 euros) (additional reporting by Terry Daley; Editing by Barry Moody/Alan Baldwin)