The Alexandria City Council unanimously approved a large business and residential development last night for Potomac Yard, once the East Coast's main railroad hub and the last major tract of undeveloped land inside the Capital Beltway.

Plans call for Alexandria's portion of the 400-acre parcel, which extends from the Braddock Road Metro station in Alexandria to Crystal City in Arlington, to have a 625-room hotel, 1,900 town houses and apartments, office space clustered around a town center and 61 acres of park.

The vote in favor of the development by Commonwealth Atlantic Properties caps a decade-long debate over the future of the old rail yard, where freight cars were sorted and sent on to their destinations. The approved plan is for roughly 10 million square feet of development, compared with earlier visions for as much as 16 million square feet. Other ideas for the yard that were tried and failed included making it the home of the new Washington Redskins stadium, or of the U.S. Patent and Trademark Office.

"We have a plan that I think is the best of all, and I would venture to say it was worth the wait," Mayor Kerry J. Donley (D) said after the vote.

Despite the smaller scale of the planned development, about a dozen of the 70 speakers at a public hearing last night spoke against the project, predicting traffic congestion and unsightly density of town houses.

"The fact is the transportation issues simply have not been resolved," said John Milliken, a consultant to the Charles E. Smith Co., which owns the majority of adjacent Crystal City.

"The new Potomac Yard will be the most dense development we will ever see," said Katy Cannady, a local civic activist and neighbor to the project.

But many citizens praised the project and the developer, hailing what they called extraordinary efforts to solicit public comment and input for the project. One elderly man rose to say he had lived a block from the yard since 1919 and approved of the project, even though he was partial to the old railroad, where he had worked for 41 years.

Specifically, the council approved four separate items last night: a master plan amendment, a zoning change, an overall concept plan and a transportation management plan.

As part of the transportation plan, the developer agreed to set aside land for a possible Metrorail station on the site. A trolley line along the Route 1 corridor also is a distant possibility.

In addition, the council expressed unanimous interest in straightening Route 1 at the site of the current Monroe Avenue Bridge, where it rises high above the old railroad yard and makes two 90-degree turns. The straightening would allow for better use of some park and school land, council members said, but critics fear it would simply invite more and faster traffic onto the already-clogged road.

The council set aside a three-acre parcel as a future site for an elementary school, despite a plea from the entire Alexandria School Board, which showed up to argue for five acres.

Commonwealth Atlantic Properties expects to go before the Arlington County Board early next year for approval of the county's portion of the development--a similar combination of office, residential and park land that would cover 100 acres. The developer predicted that the project may take as long as 20 years to complete.