Australia and Papua New Guinea are to sign a major defence treaty that could trigger mutual support in case of conflict and "integrate" forces either side of the Torres Strait.

Prime Minister Anthony Albanese will travel to Port Moresby on Monday to attend PNG's celebration of 50 years of independence and finalise the defence agreement with counterpart James Marape.

Experts are waiting to find out if the treaty will deliver a "holy grail" of security partnerships in the Pacific.

The deal will enable PNG nationals to serve in Australia's defence force with the same pay as other members and start a pathway to citizenship.

Details are yet to be revealed, including whether both countries would be compelled to consult one another if they faced a security threat, similar to NATO's Article Fo

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