The number of developers bidding on Fairfax County's controversial government center project has dropped to three, causing concern among some officials that the county's bargaining power has been weakened.

In withdrawing from the competition less than a week before the county-imposed deadline for submitting proposals, the Cadillac-Fairview Co. became the second firm to abandon its plans out of the five developers chosen by the county to bid on the project.

"I think it's terribly unfortunate because they've done outstanding work in Fairfax County," County Board Vice Chairman Martha V. Pennino said yesterday. "I would like to have had as much flexibility in selecting a developer as possible."

"I don't think it looks very good that two out of five have decided not to participate," added Supervisor Audrey Moore (D-Annandale). "I'm very concerned."

The county is seeking to enter into a joint venture with a developer in an attempt to ease the financial impact of the construction of a new government center on a 183-acre county-owned tract near Rtes. I-66 and 50. The three remaining developers must file their proposals by Monday.

Under the plan, many details of which have not been released by the county, the developer would build the government center. In return, Fairfax would give the developer up to 116 acres of adjacent county-owned land. This proposed exchange of land has generated controversy among county residents.

Four months ago, the county rezoned the area to permit the successful bidder to build up to 1.4 million square feet of commercial projects and 733,333 square feet of residential projects on the 116 acres.

The county had advertised the joint venture proposal nationwide in hopes of attracting big-name developers from across the country, but the response was viewed by development industry officials as meager and Fairfax ultimately chose five developers as finalists for the project. One of the finalists, the Donohoe Cos. Inc., withdrew last month.

Cadillac-Fairview informed the county of its decision in a letter this week. David D. Fitch, the firm's vice president, said the withdrawal was prompted by the company's purchase earlier this month of a 112-acre property for the construction of an office park and residential complex in Centreville, less than 10 miles from the proposed government center site.

Fitch said that the Centreville project, combined with the firm's large commercial project at the Capital Beltway and Arlington Boulevard, reduced the likelihood that it would be successful in developing yet a third major project in what he called the "I-66 corridor."

In the letter, Fitch said that Cadillac-Fairview, if chosen by the county, "would be unable to give the project our complete attention, given the significant number of current and planned projects we have in Fairfax County." In an interview yesterday, he said, "We would just be too deep into that market."

County Executive J. Hamilton Lambert said he was surprised by the developer's decision. He termed it "regrettable" and added, "The more competition, the better."

A spokesman for one of the remaining finalists, Turner-Harwood Ventures, said his firm had no intention of dropping out of the bidding before Monday's deadline and added that Cadillac-Fairview's decision would have no effect on its proposal.

Also expected to submit proposals Monday are the Alan I. Kay Cos. and the Charles E. Smith Cos. in conjunction with the Artery Organization.