* Swiss to vote in referendum on Sept. 26
* New law would give access to adoption, sperm donation (Adds quotes)
By Silke Koltrowitz, Brenna Hughes Neghaiwi and Cecile Mantovani
ZURICH, Sept 22 (Reuters) - Swiss voters decide on Sunday whether to allow same-sex couples to wed and adopt children after a highly charged campaign pitted gay rights activists against conservative opponents in one of the last Western European countries to still ban gay marriage.
The federal government and parliament approved opening civil marriage to same-sex couples, but opponents forced a referendum on the issue under Switzerland's system of direct democracy.
During the campaign, opponents of the reform used images of crying babies, while supporters waved "Yes, I do" rainbow flags at the Zurich and Geneva pride parades.
The share of voters set to approve same-sex marriage fell to 63% in the latest poll by gfs.bern for broadcaster SRG, while the share of those against rose to 35%, versus 69% and 29% a month earlier.
Same-sex couple Corinne Guntern and Anouk Oswald, from Zurich, said the 'Marriage for All' vote represented an important milestone for their future.
"I want to be able to choose for myself if I want to marry this partner next to me and if it's the right path for us to start a family," said Oswald, 30. "It's important to show the younger generation you don't need to hide."
Guntern, also 30, said it was not fair that a single woman could adopt a child while a same-sex couple could not.
"Today, if I reach a certain age and I'm single, regardless of my sexual orientation, I can be accepted into the adoption process and apply to adopt a child. But if I'm in a same-sex partnership, right now, I can't," she said.
"Of course, a child needs safety and love ... but I don't think it makes a difference whether that's given by a straight or gay couple," she said.
In Switzerland, same-sex couples received the right to enter civil partnerships in 2007 and the right to adopt children parented by their partner in 2018.
Under the amended law, same-sex couples would be allowed to adopt children unrelated to them.
Married lesbian couples would also be allowed to have children through sperm donation, currently legal only for married heterosexual couples. Under the law, both women would be recognised as the child's official parents from birth.
Antonia Hauswirth of the national committee "Marriage for All" said the current adoption procedure could take three years. "If something happens to the biological mother during this time, the child is considered an orphan."
The proposed scheme would give children born from a sperm donation two parents from birth and thus better legal protection, she said.
Opponents say the changes would deprive children of a father.
"Tomorrow, a child in Switzerland will still have a mother, but just an 'other parent' instead of a father. The father just gets deleted from the civil code, that's not acceptable to me," said Olivier Dehaudt, a member of a referendum committee objecting to the proposal.
The proposed legal change would also open an easier path to citizenship for the foreign spouse of a Swiss citizen.
(Reporting by Silke Koltrowitz, Brenna Hughes Neghaiwi and Cecile Mantovani Editing by Raissa Kasolowsky)
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