VIENNA, Austria (AP) _ As thousands of protesters rallied outside, members of Austria's internationally shunned center-right government joined Viennese society in waltzing the night away at this year's Opera Ball.

Some 10,000 protesters blew horns and whistles and banged pots and drums as guests arrived at the State Opera House for Vienna's premier social event.

A group of about 50 agitators scuffled several times with the police, throwing bottles and debris at the officers and hurling fireworks at the building. No injuries were reported.

The ball has frequently been the target of demonstrators decrying its extravagance and elitism. But Thursday's was the largest anti-ball protest, fueled by the outrage over the participation of the far-right Freedom Party in the new Austrian government.

Several of the demonstrators dressed in costumes, in keeping with the Carnival season _ the European version of Mardi Gras _ which in Vienna is marked by the many balls.

The most extravagant was a man dressed as Adolf Hitler, who arrived in a white Rolls-Royce and was able to get inside the building before being arrested.

Many people have compared the Freedom Party's controversial former leader Joerg Haider to Hitler, due to Haider's past statements praising Nazi employment policies and his anti-foreigner rhetoric. Haider did not attend the ball.

Even without the demonstration, the Opera Ball 2000 has suffered from Austria's political isolation and internal dissent, resulting from the coalition between the conservative People's Party of Chancellor Wolfgang Schuessel and the Freedom Party.

Leading artists and heads of state were to have been the stars of this year's ball. But the intended guest of honor, Portuguese President Jorge Sampaio, whose country now holds the European Union's rotating presidency, bowed out over the coalition issue.

Several other prominent guests, including actresses Catherine Deneuve and Claudia Cardinale, followed suit.

Special invitations were also extended to artists and opera singers, including Israeli soprano Anat Efraty and American tenor Neil Shicoff. Efraty attended, but Shicoff turned down the invitation for ``moral'' reasons. The mayors of Frankfurt, Germany and Athens, Greece also stayed away.

Earlier this week, Haider stepped down as Freedom Party head, but he remains on the board of directors and is considered to be in charge, as before.

Haider, who has led the Freedom Party since 1986, gained notoriety for past statements supportive of Waffen SS veterans and Hitler's ``orderly'' employment policies. His party rose in popularity on an anti-foreigner platform.

Freedom Party participation in the coalition has resulted in sanctions against Austria by fellow EU nations and other countries.