THERE is a school of thought that the World Trade Center museum complex should disappear altogether from its planned site at Fulton and Greenwich Streets. So the Norwegian architectural firm Snohetta, which is designing the structure, faces an extraordinary challenge: Make a 275,000-square-foot building transparent.
Transparent because it is meant to be a gateway to the memorial, which it must frame without obstructing. Transparent because it will stand between the memorial and a performing arts center by Gehry Partners, as well as a PATH station and transportation hub by Santiago Calatrava. Transparent because it will rise over the PATH mezzanine, which has been sold to the public as a luminous underground expanse.
The museum complex will house the Drawing Center, which is now in SoHo, and the much larger International Freedom Center, which is being specially created. The discussion of whether the complex ought to be moved off the site assigned to it in Daniel Libeskind's master plan has occurred largely behind the scenes.
But occasionally, the public gets a glimpse.
"The best solution is to find another contextual location for this museum, more in harmony with the rest of the buildings,'' Mr. Calatrava said last night at a program sponsored by the Municipal Art Society and the Urban Center Books store.
He said his concerns were not aesthetic but technical, in that the museum project would reduce the amount of daylight that could reach the station and limit the expanses of space that could be spanned without columns. Mr. Calatrava said he worried that placing the museum over the transportation hub would affect the staging and costs of construction and the already complex engineering of a building that will be expected to bear tremendous weight loads.
"There is enough space, enough room, to solve the problem,'' Mr. Calatrava said. "For us, it's an unbelievable difficulty to go ahead with our project if we have a technical problem of carrying an entire museum over the mezzanine."
Models of the transportation hub that were on display at the Museum of Modern Art in Queens showed nothing above the mezzanine but a pentagonal array of skylights.
Mr. Calatrava has not been alone in championing a re-examination of the museum's location at the northeast corner of the memorial precinct, which includes the twin tower footprints. One alternative is the southwest corner, at Liberty and West Streets, above an underground interpretive center.
Michael Arad, the architect of the memorial, originally called for no structures within the memorial precinct. Directed to accommodate cultural uses, he modified his entry to show a slablike building along West Street. After Mr. Arad won the competition, with the landscape architect Peter Walker, new renderings showed buildings at the northeast corner, as Mr. Libeskind intended.
Yesterday, Mr. Libeskind said the idea of a "cultural nexus" at Fulton and Greenwich Streets was vindicated by the participation of architects like Frank Gehry and Snohetta. The Norwegian firm designed the Bibliotheca Alexandrina, the new library of Alexandria, Egypt.
"It's a wonderful confirmation that interesting architects want to work there and build there," Mr. Libeskind said. "And urbanistically, it's very much part of the notion of developing, at the center of the site, something that's seven days a week."
He rejected the concept of moving the museum to the southwest corner. "First of all, it's not part of the master plan," Mr. Libeskind said. He also said such a shift would turn the somber memorial into a heavily trafficked circulation corridor for people headed to the museums, would relegate the Freedom Center to a distant corner and isolate the museum complex.
"The plan was never about stand-alone buildings," Mr. Libeskind said. "It was always about a composition that was urban." He said studies had shown that daylight could be brought down to the PATH mezzanine even with a building directly overhead.
KEVIN M. RAMPE, the president of the Lower Manhattan Development Corporation, which is overseeing the development of the memorial and cultural projects, said yesterday that Mr. Libeskind had laid out a powerful vision. "Having a corner with all these buildings and density, while preserving the memorial, is very New York," he said.
Though the corporation wants a museum building at what Mr. Rampe calls the "100 percent corner," it does not want too much of a building. In its August instructions to prospective architects, the corporation said that the design "should permit visual transparency between the surrounding sidewalks and the memorial" and that "there should also be physical permeability through the ground level."
As Snohetta interprets this mission, in the words of its Web site (www.snoarc.no), it is to design a building that is at once "unimposing yet memorable."
Unimposing yet memorable? How will they do that? What projects in their portfolio prepare them for the task?
Craig Dykers, a founding partner at Snohetta, cited the new opera house in Oslo, which is under construction. The firm lowered the building profile as much as possible, he said, to allow passersby to see over it, thereby creating a visual link among different parts of the city.
"The initial competition called for a monumental structure, and many architects interpreted this to mean a very dominating, sculptural, imposing edifice," Mr. Dykers said. "Rather than sculptural monumentality, we were interested in social monumentality."
It will be no easy matter to construct a museum over an operating multilevel transportation hub. But to the extent that he left even a sliver of an open door to rethinking the plan, Mr. Rampe added, "I don't know what the standard of proof is, but I know it has to be extraordinarily high."