Thai couple Pattanachat Monkhatha, left, and Vitaya Saeng-Aroon have been together for five years. Reuters

BANGKOK—The Thai government plans to introduce a landmark civil-partnership bill that will extend most marriage benefits to same-sex couples, a move that would put Thailand at the forefront of the gay-rights movement in most of the Asian-Pacific region.

The Thai civil-partnership bill, drafted by a Parliament-appointed committee, aims to allow gay men and lesbians who are at least 20 years old to enter into a civil partnership.

New Zealand only last month became the first country in the Asian-Pacific region to begin allowing same-sex couples to marry. Meanwhile, Vietnam said in June it is considering getting rid of restrictions that prevent its same-sex couples from marrying.

"The partnership will give [same-sex couples] rights, benefits and protection similar to most rights granted to heterosexual couples," said Naras Savestanan, director of the Justice Ministry's Department of Rights and Liberties Protection that intends to sponsor the bill.

The bill in the predominantly Buddhist country would extend such benefits as insurance, pension, tax reduction and inheritance to registered same-sex couples, without making any change the existing law on marriage. However, it wouldn't automatically allow them to adopt or have custody of children as a couple. One partner can file for an adoption individually, and those matters are handled separately under Thai law.

No group has yet to voice its opposition to the bill, but some Thais find the bill unnecessary because they contend Thai society is already tolerant.

"Introducing a new bill like this may draw negative attention to the matter that is otherwise already accepted," said Nujaree Hemapak, a 28-year-old accountant in Bangkok. "Eventually it may not benefit the [lesbian, gay, bisexual and transgender] community as thought."

The bill comes in the wake of an incident last year in which a man and his same-sex partner were denied a marriage license. Thai law restricts marriages to between a man and a woman. The couple filed a complaint to a Thai court and human-rights bodies, arguing that they were entitled to equal rights under the Thai constitution. Their fight prompted some lawmakers to form a committee to draft the country's first bill to address the issue.

Mr. Naras and members of the drafting committee launched a campaign Wednesday to gather 10,000 signatures to support the legislation, a requirement by the Thai constitution and the parliament to involve participation from the stakeholders. Gay activists expect to have no trouble obtaining the signatures in a country of nearly 65 million people.

The drafting committee doesn't have a specific time frame to introduce the bill, but said once the bill is submitted, the parliament should take about two months to deliberate it.

If the law passes, Thailand would become the first country in Southeast Asia to extend marriage-like benefits to same-sex couples. The step would highlight growing support for lesbian, gay, bisexual and transgender (LGBT) people in Thailand, where homosexuality was deemed a mental illness until 2002. Thailand repealed its anti-sodomy laws in 1956.

Unable to marry, some Thai same-sex couples have organized their own partnership celebrations or travel to western countries, such as Canada, where they can marry, said Anjana Suvarnananda, a co-founder of the Anjaree Group, which pushes for rights for LGBT people.

"Many gay and lesbian couples want to get married, but they're afraid of backlash from family, workplace and the society," said Ms. Anjana, who registered for a civil partnership with her partner last year in England, which in July approved same-sex marriages, though they aren't expected to take place until next summer.

LGBT activists said progress in Thailand and Vietnam would be a sign that the region, which has seen rapid economic growth in the past decade, is catching up with countries such as the U.S., where the Supreme Court in June extended full federal rights and benefits to married same-sex couples. More than a dozen countries now allow same-sex marriage, beginning with the Netherlands in 2001, and including Spain and South Africa.

Elsewhere in the Asian-Pacific region, little sign can be seen of near-term steps toward recognizing same-sex couples. Japan has in its constitution that marriage is for opposite-gender couples, but in 2009, the Justice Ministry allowed its nationals to marry same-sex foreign partners in countries where such marriages are legal. In May, a Hong Kong court ruled that a male-to-female transgender person could marry a man, though there is little discussion of allowing same-sex couples to marry.

In Australia, Tony Abbott's recent victory as prime minister marked a setback for supporters of a constitutional change to recognize same-sex marriage. Mr. Abbott opposes gay marriage, although he has left open the possibility of allowing a conscience vote among party members on the issue. Some state and territory legislators in Australia have proposed laws allowing same-sex marriage.

In Singapore, gay bars are allowed to operate, even though the country still keeps a law, a legacy of British colonial era, that criminalizes sex between men. The parliament argued to keep the law but promised that it won't be actively enforced.

In Indonesia, which has the largest Muslim population in the world, South Sumatra recently enforced an anti-sodomy law that criminalizes sex between men. However, elsewhere, there are some signs of acceptance for LGBT Indonesians. In the large university city of Yogyakarta, in Central Java, there is an Islamic boarding school that accepts only LGBT students. Jakarta has a shelter for elderly transgender people.

Malaysia has anti-sodomy laws that include both homosexual and heterosexuals acts.

Rights groups have been calling the country to repeal the sodomy law, charging it is used as a political weapon. In 2008, Anwar Ibrahim, leader of the Malaysian opposition, was arrested and accused of sodomy with a male former aide as his political career was on the rise. Mr. Anwar was found not guilty last year but the government is appealing the decision.

Meanwhile, the Thai tourism industry has been by marketing Thailand as a friendly destination for gay and lesbian tourists. In a campaign dubbed "Go Thai. Be Free," Thailand's tourism agency launched a promotional video that featured same-sex couples.

Thai LGBT groups support the partnership bill, although with some concerns over the lack of provision on adoption and custody of children.

"It's a small step that at least gives us some recognition, although I wish there was no barrier imposed on us," Ms. Anjana said.

For Pakorn Kueyen, a 36-year-old gay man in Bangkok, the law would provide, beyond benefits, an assurance to the LGBT community that the law is on their side and that the government is pushing for wider acceptance among conservative Thais.

"A gay or any relationship may not be sustained between two people. It needs an acceptance from family and the society to help make it last and strong," Mr. Pakorn said.

—Wilawan Watcharasakwet in Bangkok, Ben Otto in Jakarta, Celine Fernandez in Kuala Lumpur, Trong-Khanh Vu in Hanoi, Allison Morrow in Hong Kong, Miho Inada in Tokyo and Ross Kelly in Sydney contributed to this article.