* As vote nears, support for Monti group faltering in polls
* Debate on gay unions, adoption inflamed by court ruling
* Gay activist candidate for Monti quits over "smear campaign"
ROME, Jan 17 (Reuters) - Italian Prime Minister Mario Monti has said he opposes same-sex marriage and adoption, wading into an increasingly fraught debate in the home of Roman Catholicism a month before an election in which he is seeking a second term.
"My thought is that the family should be made up of one man and one woman, and I consider it necessary that children should grow up with a mother and a father," Monti told a television interviewer late on Wednesday.
"Parliament can find other solutions for other kinds of unions and cohabitations."
It was the first time the former economics professor has made a social issue part of his campaign.
Appointed as an non-political technocrat to replace Silvio Berlusconi 14 months ago and save the country from a Greek-style debt crisis that threatened the euro, Monti had previously confined himself to addressing economic issues including Italy's high unemployment and recession.
The issue of gay marriage and adoption rose to the forefront of national debate this week after Italy's highest court rejected an appeal by a father to stop his son living with his mother and her female partner, on grounds he would not have a balanced upbringing.
Monti's comments, likely to resonate with Italy's socially conservative and devout Catholic voting bloc, came as his centrist grouping faltered in opinion polls.
Support for his group fell to 14.8 percent in a survey carried out on Jan. 14 from 15.1 percent a week earlier. Support for the rival group led by Berlusconi rose 1.9 points to 26.3 percent in the same period. The poll by the Tecne research institute was released on Tuesday.
Yet Monti's stance could put him at odds with key allies. His group is likely to seek a post-election alliance with the centre-left group led by Pier Luigi Bersani, which is leading in polls but may need partners to form a stable parliamentary majority.
A key member of the centre-left group is the Left Ecology Freedom party led by Nichi Vendola, Italy's most prominent homosexual politician and founder of the country's first gay rights organisation.
Vendola, previously criticised by Monti as conservative for opposing the liberalisation of hire-and-fire laws, responded ironically to Monti's comments on Twitter: "According to Monti, the only family is one composed of a man and a woman. Who's the conservative now?"
Monti's campaign was endorsed last month by the Vatican's newspaper L'Osservatore Romano, which has been increasingly vocal in its opposition to same-sex marriage in recent months.
A rally against French government plans to legalise it drew thousands in Paris on Sunday.
The Vatican, which opposes the social acceptance of homosexuality and same-sex relationships, was targeted by topless women protesters on Sunday who shouted "Homophobes shut up" as Pope Benedict gave his weekly service to pilgrims in St. Peter's Square.
The outgoing prime minister's comments coincide with the withdrawal of a gay activist who was a candidate for Monti in the Senate.
Alessio De Giorgi withdrew his candidacy after what he called a "media smear campaign" by a right-wing newspaper, which had published a photo of him with a transvestite and reported that gay escorts were selling their services through an internet site he owns.
"I was put through the meat grinder," De Giorgi said on his campaign website. (Reporting by Naomi O'Leary; Editing by Tom Pfeiffer)