Current Attorney-General Chris Finlayson wanted to overturn New Zealand's anti-nuclear legislation without a public vote, a WikiLeaks cable reveals.

The cable from February 2006 describes a move to change National Party policy to unreservedly support anti-nuclear legislation introduced by Labour in 1984.

Despite the policy change, many National MPs privately supported overturning the anti-nuclear legislation, the cable says.

Of those Mr Finlayson - then a rookie MP - is cited as supporting an immediate end to the ban on nuclear ships entering New Zealand waters.

"We know only one National MP - the newcomer Chris Finlayson - who thought a National Government should change the legislation right after winning an election, without a referendum. But he also thought the Government should then shelve the issue by not encouraging or allowing any ship visits for a number of years," it says.

National changed its policy to endorse anti-nuclear legislation after the 2006 meeting described in the cable from US Ambassador Bill McCormick.

Its previous policy of supporting a change if a referendum found there was public support for the move had been attacked by Labour.

The cable says the policy change was motivated by a need to create a political defence against those attacks, rather than broad ideological support for the move from within the party ranks.

Foreign Minister Murray McCully admitted the decision came on the back of National Party polling showing the "nuclear issue" had cost votes, it says.

"(McCully) said if National and Labour both agree that the ban should remain in place, National can better focus attention on Labour's gratuitous anti-American statements and overall failure to improve relations with the United States," it says.

A spokesman for Mr Finlayson did not respond to calls for comment.

Wikileaks cables show the US urging New Zealand to water down its anti-nuclear legislation.

Top US Navy chief Admiral William Fallon urged then Defence Minister Phil Goff and Prime Minister Helen Clark to reduce the sensitivity of the issue during his January 2006 visit to New Zealand, a cable says.

Ms Clark and Mr Goff reponded that the anti-nuclear issue had become an untouchable political "third rail", it says.