New Zealand and the United States will exchange diplomats on secondment under an arrangement to be signed on Friday, putting the two countries in an even closer relationship.
US Secretary of State Hillary Clinton and Foreign Minister Murray McCully will sign the agreement in Auckland on the first day of Mrs Clinton's three-day visit to New Zealand.
Government officials said today it meant New Zealand would join a select group of trusted countries with close ties to the US.
Diplomats being posted to New Zealand's embassy in Washington would be able to spend 12 months working at the State Department, and American diplomats coming to Wellington would be seconded to the Ministry of Foreign Affairs and Trade.
Mrs Clinton will be making her first visit to New Zealand, in any capacity, when she arrives early on Friday.
She will hold talks with Prime Minister John Key and Mr McCully at Government House in Auckland before signing the diplomatic agreement and holding a press conference.
Mr Key will host a dinner for Mrs Clinton on Friday night.
The talks would be wide-ranging, officials said, covering the situation in Afghanistan, regional issues and trade.
It has been reported that Mrs Clinton would announce a resumption of joint military exercises, which are on hold because of New Zealand's anti-nuclear policy, but the officials said no such announcement was expected.
It would be outside Mrs Clinton's portfolio, and no defence officials would be in her 40-member delegation.
Mrs Clinton will meet Labour Party leader Phil Goff on Saturday, attend a reception hosted by the NZ-US Council where she will meet business leaders, and take part in a ceremony to mark the "virtual opening" of a joint wind turbine project on Ross Island in Antarctica.
The turbines will supply 15 percent of the power for Scott Base and the American McMurdoe Station.
Before leaving on Sunday, Mrs Clinton will attend a dialogue forum with a range of people and lay a wreath at the Auckland War Memorial Museum.
Her visit this early in the life of the new US administration is seen as evidence of President Barack Obama's wider foreign policy perspectives, which include strengthening links in the Pacific where China has been flexing its diplomatic muscles.
The New Zealand officials said there had already been extensive engagement with the new administration, particularly on defence matters.
They said it was recognised that the nuclear-free legislation, which is preventing US Navy ship visits, was going to remain a point of difference but that did not determine the overall course of the relationship.
Mr Key has met President Obama three times, and is expected to take up an invitation to visit Washington during the first half of this year.
Mrs Clinton will also visit Honolulu, Papua New Guinea, Canberra, and Melbourne.