For months, it was as a resilient symbol of what the terrorists could not bring down: nine stories of the World Trade Center's north tower facade stood in the rubble while workers recovered bodies and cleared the site of the towers' ruins.

When workers brought the latticework facade down in December 2001, officials said some of it would be saved. Relatives of the victims say they want to one day return the steel columns to ground zero to become part of a memorial.

But officials now say they aren't sure how much of that 100-foot-tall, 80-foot-wide facade they have and what can be put back together.

The Port Authority of New York and New Jersey, which owned the trade center and carted thousands of tons of trade center steel to an airport hangar for storage and cataloguing, recently hired a structural engineering firm to determine what's left of the widely photographed facade.

"We're trying to just find out what we have," said Monica Svojsik, a senior associate at a firm run by Leslie Robertson, the structural engineer for the trade center when it was first built.

Svojsik said she has been examining the steel columns in storage at a John F. Kennedy International Airport hangar for markings that would identify where they came from in the trade center, and whether they are part of the facade.

Several of those columns, including the distinctive, three-pronged trident columns that anchored the trade center towers, have been located and identified as part of the historic facade, although no steel pieces have yet been found that fit together, Svojsik said.

Almost all the other steel, including the 62-ton skeletal remnants of a south tower facade that also became an iconic image after the attacks, was sent to scrap yards.

The Port Authority hired architects in 2001 to find historically significant pieces of steel at ground zero, and tag them for removal to the hangar, said agency spokesman Steve Coleman.

Based on the original plans for the towers, Coleman said, the agency believes it may have saved 40 percent of the facade. It has hired the engineers to look at the columns "and definitively identify where they came from and how they might fit together."

Bart Voorsanger, who headed the team of architects that retrieved trade center steel, said resurrecting the facade was "not impossible," but would likely cost several million dollars. He said it would be challenging because the beams were so large and, in some cases, cut at different angles by various welders who volunteered their services in the months after the attacks.

That was a blow to victims relatives, since officials had said over the years that the steel of the facade had been saved and marked for reassembly.

"From what we were told, it was tagged in a way that it could be potentially reinstalled," said Anthony Gardner, whose brother died at the trade center. Gardner and other family members have sought to return a large part of the facade to street level when a memorial is built over the next few years.

The surviving columns of the destroyed towers remain the most enduring image of the towers' destruction, Gardner said, because "they were leaning, but they never fell. ... It survived and stubbornly stood, despite the devastation."

Voorsanger said once the steel beams were moved to the airport hangar, "we were not laying it out as if it were going to be re-erected in a pattern."

The Port Authority and a federal agency that investigated the towers' collapse were the only agencies to save any trade center steel, Coleman said. Most was sent to scrap yards and recycled.

Joe Daniels, acting president of the World Trade Center Memorial Foundation, which is developing museum and other exhibits for the memorial, said the foundation planned to include iconic artifacts like the facade in memorial plans.