The Liberal Party's first openly gay federal politician says a postal vote plebiscite on same-sex marriage would be "acrimonious" and "divisive" as the issue further inflames tensions within the Turnbull government.

West Australian senator Dean Smith said the proposal, led by the government's leading conservative figure Peter Dutton and backed by former prime minister Tony Abbott, was an acknowledgement the issue must be resolved this parliamentary year.

"I think this is an important step because it's a demonstration by Peter Dutton that there is a will on the part of the government to bring this matter to a close," Senator Smith told ABC Radio on Tuesday morning.

But a postal vote plebiscite was not the way to resolve the matter, he said.