* Irish Times poll shows 2-to-1 margin in favor
* Two other polls show support over 60 percent, third closer
* All main political parties support measure (Updates with Sunday newspaper polls)
By Conor Humphries
DUBLIN, May 16 (Reuters) - Irish voters are set to back the introduction of gay marriage by a margin of as much as two-to-one next week and become the first country to approve the policy in a national plebiscite, a series of polls indicated on Saturday.
Long considered one of the most socially conservative countries in Western Europe, support for gay rights has surged in Ireland in recent decades as the power of the Catholic Church collapsed in the wake of a series of child abuse scandals.
The Irish Times poll of 1,200 voters showed 58 percent planned to vote in favor of the measure compared to 25 percent against and 17 percent undecided.
Two more polls to be published in Sunday newspapers put support for the constitutional change above 60 percent, while a third saw the advantage of the Yes side slip to 53 percent with 24 percent opposed and almost as many undecided.
Analysts have said the fall in support in some of the polls is nowhere near as sharp as the decline in support for divorce in a 1995 referendum, when that Yes campaign's 44 point lead disappeared as conservative campaigners spoke out in the last weeks of campaign. The measure was approved by 50.3 percent.
Long a taboo in a country that only decriminalized homosexuality in 1993, gay rights have been championed by all the main political parties.
Prime Minister Enda Kenny was widely praised for appearing at a prominent gay bar last year at an event for gay members of his Fine Gael party.
The campaign has led to a number of high profile figures announcing publicly that they are gay, including the country's health minister and a prominent television journalist.
Campaigners against gay marriage have made some gains after warning that it might lead to an increase in adoptions and surrogacy births involving gay couples. Yes campaigners reject the claims.
In letters published on Saturday, a number of Catholic bishops, who have played a low key role in the campaign, warned their parishioners that the vote could profoundly change the understanding of marriage, family and parenthood.
Same-sex marriage was allowed for the first time in the United Kingdom last year, but it is still not permitted in Northern Ireland, where the Democratic Unionist Party of First Minister Peter Robinson has campaigned against it.
Irish voters go to the polls on Friday, with the results of the referendum expected the following day. (Additional reporting by Padraic Halpin; Editing by David Clarke and Alan Crosby)