A proposal to bring streetcars to the Route 1 corridor between the Pentagon and the heart of Alexandria is drawing tepid reviews from Alexandria officials, who question its expense and its value to city residents.

A week ago, Arlington County Board member Chris Zimmerman (D) and Alexandria City Council member Lois Walker (D) held a news conference to highlight the idea, which was first developed as part of an $11 billion package of Northern Virginia road and transit improvements. Because the area is already congested and because a massive new development at Potomac Yard is about to worsen that congestion, they said, something more than the current Metrorail line is necessary.

"Light rail is a particularly good mode of transportation for the type of community that is here and will be developed here," Zimmerman said.

Walker touted the trolleys, which she called an effective way to "move as many people as we can within the same corridor."

But other Alexandria officials were singing a different tune.

"It's very expensive, and it doesn't really solve commuting problems," said City Manager Vola Lawson.

Mayor Kerry J. Donley (D) said that all transportation ideas for the corridor are still on the table, but that the light rail's estimated $400 million price tag is a big issue.

"We can't go about this project without recognizing the tremendous cost that may be there," he said.

The area encompassing Reagan National Airport, Crystal City and Pentagon City is the subject of much debate, since its last large patch of open space will soon disappear.

Commonwealth Atlantic Properties is about to break ground in the old rail yard for a massive project. The Alexandria side could include 5.5 million square feet of development and the Arlington side 4 million, both pending approval from local governments. At completion, projected to be 20 years away, the area would hold about 5,000 residents and 25,000 workers.

Initial plans for the Alexandria site called for much denser development, and officials assumed a new Metro stop would be part of the package. But the Metro idea has lost favor, and current transportation plans include two spine roads through the development, a possible straightening of the Route 1 bridge over the rail yard, and bus service.

Even if a Metro stop were built on the Alexandria side, Zimmerman said, it would be too far away to serve Arlington residents. Lawson added, "I think the Metro station in Alexandria benefits us more, and the light rail benefits Arlington more."

The assessment from Alexandria's transportation officials also weighs against the trolleys.

"Light rail and Metrorail are fairly expensive transit options and generally would be associated with higher-density development," said Dave Ruller, deputy director of transportation and environmental services.

Zimmerman and Walker praised the more expensive light rail system over buses because trains have greater capacity and less pollution and are preferred by the general public. The trains would travel either in the right lane of the road, like a bus, or down the middle of the road, between lanes of traffic.

A number of configurations are possible. The trolley could travel along Route 1 or along a planned road in Potomac Yard, connecting to existing roads in Alexandria and Crystal City. The two end points of the trolley would be Alexandria's Braddock Road Metro station and the Pentagon.

Funding would come from federal, state and local moneys, as well as private sources, Zimmerman said, adding that the creation of a special commercial tax district is one possibility. But Alexandria's portion of that tax district would provide only $1.2 million annually, according to Mark Jinks, the city's finance director.

And although Zimmerman said that Alexandria and Arlington would benefit equally from the light rail, Jinks said his early estimate for Alexandria's contribution was just $105 million, or little more than one-fourth.

Walker said she was undeterred by the obstacles but acknowledged that announcing the project was the beginning of a long road.

"I have to persuade City Council," she said.