ROME (Reuters) -- Italy's supreme court upheld a corruption conviction against a close ally of outgoing Prime Minister Silvio Berlusconi on Thursday and handed a six-year prison term to Cesare Previti for passing on bribes to judges.

Berlusconi and his business empire were not involved in the case but the two men's legal woes are entwined and they have both regularly accused the Milan magistrates of pursuing them for political motives.

Supporters of Berlusconi, who was dogged by corruption trials during five years in power, leapt on the decision, saying it was linked to the defeat of his center-right coalition in elections last month.

"The era of the center-left starts here," Berlusconi's former lawyer Carlo Taormina, a member of the media tycoon's Forza Italia (Go, Italy!) party, told reporters.

Thursday's verdict is a bitter blow for Previti, a Forza Italia MP who has spent the past 10 years fighting the accusations in Italian courts.

Previti, who was defense minister in Berlusconi's first government in 1994, has no right of appeal but it was not yet clear whether he would go to prison.

Under a law passed by Berlusconi's government, judges can instead put him under house arrest because he is more than 70 years old. The law, which came to be known as "Save Previti", was passed shortly after he turned 71 last year.

"We have been left alone in this battle, abandoned by everyone," said Alessandro Sammarco, one of his lawyers. --------Legal spotlight

Previti's conviction has no direct effect on Berlusconi but a separate decision by the supreme court on Thursday touches more directly on the media tycoon.

The court, in the surprise ruling, said it had asked for a corruption case involving Berlusconi's Fininvest media empire and his publisher Mondadori to be reopened at the appeals stage.

Berlusconi himself cannot be re-tried in the Mondadori case because a statue of limitations has kicked in, but it returns his legal wrangles to the spotlight just as he is trying to regroup the center-right before administrative elections.

He is also trying to undermine Prodi's candidate and promote his own for the prestigious post of Italian president.

The court's decision will also heighten speculation that Berlusconi and his Mediaset business empire may face difficulty now that its founder is out of power -- something Mediaset executives worked to play down in the run-up to the vote.

Previti's conviction centers on his part in passing on millions of euros in bribes to judges to help win a favorable ruling in a 1990s takeover case involving petrochemical firm SIR.

Judges described the SIR case in 2003 as "the biggest case of corruption in the history of the Italian republic".

By contrast, the Mondadori case centers on alleged bribes to judges passed through Berlusconi's media empire in the early 1980s to help the tycoon in a business battle against his long time foe Carlo De Benedetti.

Berlusconi has always denied the charges.