The navy scotched a proposed visit to New York by a nuclear submarine named after the city for reasons including the density of New York's population and the threat of terrorist attack.

Although the U.S. government encourages its allies around the world to accept port visits by U.S. nuclear warships, there are some U.S. ports where public safety factors play a part in ruling out visits, Pentagon officials acknowledge.

The navy discusses the procedures governing port calls by nuclear ships with great reluctance and with language that seems designed more to obfuscate than enlighten.

In essence, an official Navy statement said the procedures determining where nuclear-powered warships call are classified.

"There are many factors which are considered in making these determinations, including reactor design, personnel training, operational practices, the ship design, public health and safety and, very importantly, the military necessity of the visit in order for the Navy to carry out its mission," said the Navy statement in reply to a reporter's question.

A visit to New York by the recently commissioned nuclear submarine named for the city was proposed and met with the approval of city officials.

"The men and women of the U.S. Navy are always welcome here and so are their ships," Mayor Edward Koch said.

However, the danger of an attack by terrorists in New York and the density of the city's population were cited in the decision not to allow the submarine to put in to New York, according to defense officials.

The decision seems somewhat inconsistent because nuclear-powered warships visit other large cities - including San Francisco, San Diego and Long Beach, which is near Los Angeles. The Navy refused to provide a list of ports that are off-limits to nuclear ships.

In addition, there have been no reported incidents with the nuclear power plants aboard Navy ships and there is no apparent reason to think that they are unsafe - for New Yorkers or anyone else.

Although the Navy refused to spell out why New York is different from other cities, there have been other occasion when nuclear ships were kept out of New York.

During the international naval review that accompanied Operation Sail as one of the most successful of American bicentennial activities on July 4, 1976, 22 U.S. warships visited New York, including one of just about every type except nuclear submarines and nuclear surface ships.

One nuclear-powered warship, the submarine Nautilus, has visited New York. It came in 1958 after a transpolar voyage.

The decision about the submarine New York City was made before the Three Mile Island accident that focused attention on the dangers of nuclear power.

A confidential cable from Assistant Secretary of State Richard Holbrooke to Armistead Selden, then U.S. ambassador to New Zealand, in early April illustrates the concern of U.S. policymakers that other nations receive nuclear ships and the sensitivity of the issue after the nuclear power plant accident at Three Mile Island, near Harrisburg, Pa.

". . . We all agreed that your departure statement would provide an ideal occasion to establish clearly and authoritatively in the New Zealand public record the link that must be made between [nuclear-powered warship] visits and the viability of ANZUS" (the Australia, New Zealand, U.S. defense pact), Holbrooke cabled the ambassador, who was preparing to end his tour of duty in Wellington.

"In recent days, however, we have had to think very seriously about whether your planned remarks would move us closer to this long-term objective or produce a short-term setback because of current world focus on the Three Mile Island incident.

"We believe that, at this time, the message we want to deliver about our common security interests is all too likely to be drowned out by the voices of those who would use your speech as a pretext to transfer current levels of concern over nuclear safety . . . into an attack upon the [New Zealand] government's policy of allowing [nuclear ship] visits," the cable said.

Nuclear warship visits have been a major issue in New Zealand because the opposition Labor Party headed by Wallace Rowling has as a part of its platform a ban on such visits and did not permit them when it last was in power.

A New Zealand official said the U.S. government has implied that there must be a link between the defense umbrella of ANZUS and New Zealand's cooperation in receiving nuclear warship visits, but that it has not been explicit publicly.

Protest demonstrations have greeted nuclear warships in Australia, Japan and other countries, but U.S. allies have accepted the American position that such visits are a part of the role allies must play when they enjoy defense arrangements with the United States.

Since about 40 percent of the Navy's major combatant ships are nuclear powered, it is increasingly important for the United States to have the flexibility for nuclear ships to visit many countries around the world, a State Department official said.

"Nuclear propulsion is not much of an issue," the official continued. "From the political point of view, we don't see any real problem."

The Holbrooke cable promises that the State Department will look for an opportunity to deliver its message to New Zealand "at a point when the fears and emotions generated by the Three Mile Island incident have receded somewhat."