Europe's main gay pride festival comes to Rome on Saturday with organisers hoping the presence of Lady Gaga will help amplify their message of defiance against the Vatican and Prime Minister Silvio Berlusconi.

The US singer is to address what organisers say will be over one million participants with a message of support for gay rights in Italy, which lacks legislation against homophobic attacks and does not allow gay civil unions.

‘This is the most backward government Italy has had since World War II,’ said Paolo Patane, director of Arcigay, an activist group founded in the 1980s that is helping to organise the EuroPride parade in the Italian capital.

‘It's a government in which the prime minister goes with underage girls but then says that parliament will never approve legislation that contradicts the concept of the family promoted by the Vatican,’ he said.

Mr Patane pointed out that the mass gathering in Rome also comes just days after Mr Berlusconi suffered a major defeat in local elections and said he hoped it would help ‘push out this backward government.’

The EuroPride parade will make its way through the city centre and end with a concert and rally in the Circus Maximus, an ancient Roman arena.

Police are expecting around 500,000 people to take part.

Lady Gaga has Italian-American roots and has long lobbied for gay rights in the US.

The run-up to Saturday's event has been marred by some small anti-gay protests around a fair set up by organisers near Rome train station.

Vladimir Luxuria, the organiser of Italy's first gay pride festival in 1994 and a former member of Italy's parliament, said homophobia is on the rise.

'This parliament is homophobic. The fish stinks from the head and we have a prime minister who is a gay-basher,' said Ms Luxuria, a transsexual who has just published a novel linking homophobia in World War II to the present day.

Mr Berlusconi has long been notorious for his off-colour quips and last year dismissed a sex scandal involving him with a homophobic comment saying: 'It's better to be passionate about beautiful women than to be gay.'

Activists quickly came up with a slogan printed on placards and T-shirts reading: 'It's better to be gay than to be Berlusconi.'

In another speech in 2007, Mr Berlusconi boasted there were no gays in his party.

'Don't be afraid - the gays are all on the other side,' he said.

Mr Berlusconi is on trial for paying for sex with a 17-year-old girl and then allegedly abusing the power of his office to try and cover it up.

His former wife said she was divorcing him because he 'frequents minors'.

The prime minister has repeatedly denied all the accusations.

Mr Patane said the real challenge for gay rights, however, is the continued role of religion and 'the Vatican hierarchy' in European societies.

The Vatican condemns homosexuality and has lobbied hard against legislation allowing more gay rights, including marriage and adoptions.

Pope Benedict XVI defended traditional family values during a visit this month to Croatia where links between politics and religion are strong.

'Do not give in to that secularised mentality which proposes living together as a preparation, or even a substitute, for marriage!' he said in a homily.

He also urged lawmakers to introduce legislation that 'supports families in the task of giving birth to children and educating them.'

Asked to compare the current EuroPride festival to the first one that she organised, Ms Luxuria said that while the numbers of people attending such events have increased drastically, Italy is still stuck in the past.

‘I'm very sad that there are gay Italians who say they are forced to leave because they're gay,’ Ms Luxuria said.

She added: ‘Now the costumes are less provocative because the situation really is serious.’