New York developer Larry Silverstein may be close to landing his first pair of tenants for 7 World Trade Center, two years after he began trying to fill the tower on the northern edge of Ground Zero.

The New York Academy of Sciences, a nonprofit organizer of scientific conferences, is in talks about taking space, said Fred Moreno, its communications director. Minneapolis-based Ameriprise Financial Inc., a financial planning service spun off from American Express Co., also may rent space, said its spokesman, David Kanihan.

Silverstein's difficulty finding tenants for the building, the first skyscraper to be built at the scene of the Sept. 11, 2001, terrorist attacks, has raised concerns that he will be unable to fill the 11.7 million square feet of office space at 7 World Trade Center and at the new trade center site. The towers have been estimated by Silverstein to cost $8.3 billion.

"Two cherries don't make a pie," Myers Mermel, chief executive of TenantWise, a Manhattan real estate brokerage, said yesterday. "Silverstein needs to refocus on attracting larger financial services firms" for the 52-story, 1.7-million-square-foot tower due for completion in early 2006, he said.

Bud Perrone, a spokesman for Silverstein, and Bob McGrath, a spokesman for Silverstein's leasing broker, CB Richard Ellis Group Inc., declined to comment.