The Alexandria City Council rejected plans for the $500 million Potomac Greens office project last night despite expectations that the developers will sue the city over the decision.

Because the 16-building complex along the George Washington Memorial Parkway would comply with zoning regulations, the developers contend that the city had no legal basis for rejecting the plan.

"We have been unfairly treated," said Julien Redele, chairman of the Savage/Fogarty Cos., which has joined with the Richmond, Fredericksburg & Potomac Railroad in the project. "Our legitimate legal rights have been denied, and we have no option but to go to court."

Potomac Greens, a 2.3-million-square-foot project, was to sprawl over 38 acres west of the parkway near Daingerfield Island.

Traffic was widely considered its biggest problem. City planners said the office complex could attract 3,700 vehicles during morning rush hours.

Council members voted unanimously to reject the plan, saying it was "out of scale" and "damaging to the health and welfare of residents" and that it did not include a traffic management plan.

Last month the city passed a law requiring developers of large projects to reduce by 10 to 30 percent the traffic the projects would be expected to generate. The ordinance requires a written plan detailing how developers would reduce traffic by providing Metro shuttle buses, vans and free parking for those who car pool.

The Potomac Greens developers did not file a traffic management plan, contending that the law did not apply to the project because it was passed after they filed their site plan. Alexandria City Attorney Philip Sunderland disagreed.

Mayor James P. Moran Jr. called the project "the most egregious threat to the integrity of the parkway and livability of the city."

Moran said he believed the developers would file suit, but eventually, he predicted, they will return to the council with a more palatable plan.

About 100 citizens crowding the council chamber applauded the decision.

"For those of us living in the northeast tip of the city, the traffic implications of the Potomac Greens development hang like a knife, threatening to cut us off from {the rest of} Alexandria entirely," Terri Hauser said.

Hauser, representing the 283-unit Marina Towers condominium association, said the project would "trample rights of citizens" and "take away the value of our Alexandria city address."

Civic activist Ellen Pickering said the complex would destroy the parkway. Further, she said, the damage would not be limited to the road: "If you pinch the artery of the city, you kill the city."

Carson Lee Fifer Jr., attorney for Savage/Fogarty, argued that the city's staff had recommended approval of the site plans if the developers met 44 conditions. "We agreed to 35 of them," Fifer said, and the developers offered "reasonable alternatives" for the remainder.

Last night the developers offered to grant a 10- to 13-acre easement of scenic open space to the National Park Service. Previously, they had offered to largely finance a $19.2 million Metro station on the site between National Airport and the King Street station.

Still, the offer was considered not good enough. Offices generate far more traffic than residential units, one reason the city desperately wanted the developers to include apartments or condominiums in their plans.

"I think basically we're talking about the health and welfare of citizens," said Vice Mayor Patricia S. Ticer. " . . . It's out of scale."