Hubert K. Hoffman, a developer vying for a contract to provide office space for 20,000 Navy workers, has offered to pay the City of Alexandria $140 million over 30 years to make up for tax revenue the city could lose if the Navy moves to Hoffman's proposed site in Eisenhower Valley.

Hoffman, one of five Northern Virginia developers seeking to build the $861 million Navy project, said he made the offer in response to concerns by Mayor James P. Moran Jr. and other city officials that the federal government's plan to own the project site would cost Alexandria millions of dollars a year by removing the property from tax rolls. Federal land is tax-exempt.

In return, Hoffman is asking the city not to go through with plans to restrict building density guidelines on a 20-acre tract near his proposed site for the Navy. The City Council will consider the restrictions Monday.

Hoffman plans to donate a 13.9-acre site to the federal government if his site is chosen for the Navy project.

Moran said yesterday that although Hoffman's proposal appears to alleviate some of Alexandria's concerns, other questions remain, including how to handle the traffic that such a huge facility would bring to the Eisenhower Valley.

"Traffic is still a major issue with this proposal," Moran said.

The Navy proposal, which calls for more than 3 million square feet of office space, is the largest project in a 30-year, $3 billion General Services Administration building plan. The federal government's effort to consolidate workers from 20 facilities into one is being prompted primarily by the expiration of long-term leases -- most of them with buildings in Crystal City -- that in some cases have given the government cheap office space.

Instead of leasing more space, the government is seeking to own the Navy's new facilities, a move that officials say could save hundreds of millions of dollars compared with a lease or a lease-to-own arrangement.