The first version of the Freedom Tower was unveiled in 2003 and publicly embraced by city and state leaders, including officials of the Port Authority of New York and New Jersey, which owns the site. The design placed the building as close as 25 feet from West Street-Route 9A. From a parallelogram base ringed by an arcade of exposed columns, the tower was to twist as it rose, culminating after 70 floors of occupied space in an open-air superstructure of cables, power-generating windmills and an off-center spire meant to echo the Statue of Liberty.
People who have been informed about the redesign discussions say that the architects will probably set the building back at least twice as far from the street to limit blast damage from a car or truck bomb, and untwist it. The new building is likely to have a square floor plan, with a different summit and several more occupied floors than were in the original design. Windows below the 150-foot level will almost certainly be fewer and smaller, and views will be limited. The arcade around the base may be eliminated.
Managers of the redevelopment insist that the trade center site can be made safe through a series of protective zones, with checkpoints, bollards and other barriers.
And they say the Freedom Tower and other sensitive buildings can be hardened with blast-resistant materials. Some, like Daniel Libeskind, the site's master planner, say the new World Trade Center ''will be as safe as any site in the world today, if not safer.''
''We are responding to the need for security, but we are also responding to life,'' Mr. Libeskind added. ''We cannot make the Freedom Tower a tower of fear.''
There is no denying, however, that this site has been attacked twice. In this context, the assessment of security is something of a gamble against unknowable, and possibly deadly, odds.
Much about security preparedness has been deliberately shrouded in secrecy. Some experts and public officials spoke anonymously for this article because they are forbidden contractually, or by the agencies they work for, to publicly discuss questions of safety. They also say that specifying security details is an invitation to terrorists to exceed them.
Some with knowledge of the Police Department's evaluation of risk on the site said that its experts favor caution in security tradeoffs, but do not want to be unrealistic in demanding assurances of absolute safety. These experts acknowledge that an urban site cannot be built that is totally immune from attack, but insist that its buildings must not be so vulnerable that they invite an attack.
The Freedom Tower's original ''threat and risk assessment'' report, these experts say, specified that the building achieve the security standards for a high-level government structure in Washington, capable of resisting a 5,000-pound truck bomb -- more than the size of the 4,000-pound Oklahoma City explosion in 1995.
Though such criteria were unusually high for an office building, the police rejected them as inadequate, given the Freedom Tower's height, its role as a political statement, its planned glass exterior and its proximity to West Street-Route 9A.
The police did suggest some redesign options and submitted a report detailing the history of truck-bomb attacks, according to some with knowledge of the ensuing dialogue. Finally, in early May, the governor announced that the Freedom Tower would be moved away from West Street, and that the tower exterior would be strengthened.
Untwisting the torqued design of the original tower would reduce the size of the building's base, and help meet the Police Department's requirement that it be set back farther from the street.
The original distance of 25 feet from West Street-Route 9A will be doubled, at a minimum; as much as 65 feet is conceivable. Since the distance from Vesey and Fulton Streets will be considerably less, traffic on those streets will most likely have to be limited.