Arlington officials have sharply criticized as erroneous and inadequate parts of a federal government study of a proposal to build new offices for thousands of Navy workers in Northern Virginia.

County Manager Anton S. Gardner said the study generally overstated the tax benefits of the project while understating or ignoring the costs local government would have to bear in building parks, roads and sewers to accommodate the huge complex.

Arlington officials were particularly upset by the study's conclusion that the Navy project, by bringing in more workers and related businesses, would be profitable for Arlington's tax coffers. That would happen even if the Navy owned the complex and, as a federal agency, did not have to pay any local taxes, the study said.

Navy ownership of its facilities would remove between $400 million and $750 million from Arlington's existing and future tax base, a report by Gardner said.

"A more realistic projection . . . would show that the county would be negatively impacted" if the Navy owned rather than leased its offices, Gardner said.

The Navy proposal would consolidate thousands of workers now at 20 locations in Northern Virginia. About 16,000 Navy workers currently use leased offices in Crystal City in Arlington.

Congress has authorized $240 million to build the first 1 million square feet of the proposed 2 million-square-foot project.

Three of the sites under consideration are in Arlington. The Arlington choices are renovating the Navy's current space in Crystal City; building new offices in Crystal City and next door in Pentagon City, and a complex proposed for Port Potomac land just south of National Airport.

The other four sites being considered are in Alexandria.

Another sticking point with Arlington officials is the effect the huge complex would have on traffic.

The federal study estimated road improvements at the various sites would cost from $49 million to $162 million. But the report never specified who would pay the bill.

The study also wrongly assumes that public park areas could meet the demands of the new workers, Gardner said. And while the study notes that a new fire station would be needed, it does not say who would pay for it.

Gardner suggested that the General Services Administration, which commissioned the two-volume study, order major revisions of the findings before a decision is made on where to put the massive complex.

The GSA is expected to issue a final version of the study this fall and make a decision on where to put the office complex by the end of the year.