The Alexandria City Council, further expanding the city's development along the Capital Beltway, last night approved a major residential and office complex for the Eisenhower Valley, one of the largest undeveloped tracts remaining in the city.

In a 5 to 1 vote, the council approved the million-square-foot Mill Race project, which is expected to cost $80 million to $100 million and to be completed in three to five years.

The complex, proposed by a partnership of four Alexandria businessmen -- James Hayman, Monty Duncan, Jeffrey Yates and Jason Yates -- and Bush Construction Corp. of Norfolk, will include five high-rise residential buildings and an office complex on a 5.15-acre site off Eisenhower Avenue and Mill Road.

The buildings, from 15 to 25 floors, will be among the tallest in the city. A total of 645 condominium apartment units are planned for the project.

Mill Race is the latest of several huge projects proposed for the Eisenhower Valley, a four-mile corridor that parallels the Beltway between Route 1 and Van Dorn Street, and the first project intended to be primarily residential.

The area, long considered a gold mine because of its proximity to the Beltway and Metrorail, is composed largely of old rail yards and industrial sites and is isolated from the rest of the city. That isolation will soon give way to one of the most densely developed sectors of the 15.7-square-mile city.

In April, the council unanimously approved a billion-dollar proposal by the Oliver Carr Co. and Norfolk Southern Corp. That project, just east of the Mill Race site, will include more than 1,000 residences and more office space than the Pentagon.

Voting in favor of the Mill Race project were Vice Mayor Patricia S. Ticer (D) and council members Kerry J. Donley (D), T. Michael Jackson (D), Lionel R. Hope (D) and William C. Cleveland (R).

Voting against was Redella S. "Del" Pepper (D), who said she was concerned about the density and height of the buildings. Mayor James P. Moran Jr. (D) was absent for the vote.

According to several council members who favored the high-density project, approval hinged on proximity to the Eisenhower Metro station, which lies within 1,000 feet, and the developers' agreement to provide affordable housing and a mixed-use development.

"This approval brings us to a crossroads," said Donley. "This is a signal to other developers that we will encourage mixed-use, that we will encourage affordable housing." "We do not want to create a death valley after 5 p.m.," he said.

The council's action came after a public hearing at which no residents spoke against the proposal. However, not everyone in the city is applauding the project.

Gil Zimmerman, director of the Old Town Civic Association, said that it was clear that the council would vote for the project.

"It was thought that no good purpose would be served by beating a dead horse," Zimmerman said.

In other business, the council heard two taxpayer organizations' concerns about the city budget process and taxes.

A spokesman for Alexandrians for Responsible Taxation and Spending, concerned about the council's recent decision to increase the utility tax paid by businesses, called on city officials to make the budget process more open and announced that it had formed a panel to examine expenditures, revenue and the distribution of Alexandria's tax burden.

A spokesman for the Alexandria Taxpayers Alliance called for a freeze on real estate taxes and for the council to use any additional revenue it receives from Potomac Yard for tax relief.

A recent Virginia Supreme Court decision forces the Richmond Fredericksburg & Potomac Railroad to pay more taxes on the switching facility, which is near National Airport.