The Arlington County Board has approved construction of a $40 million, Kuwaiti-backed luxury condominium complex for the Rosslyn area, bringing high-rise development to the backdoor of one of the county's oldest garden-apartment communities.

In an action that some board members said was troubling, the board agreed to plans by Knightsbridge Development Co. Inc. to build a 14-story complex of 357 apartments near the Colonial Terrace neighborhood, a short walk from the Rosslyn Metro station. County officials traditionally have taken pride in protecting Colonial Terrace, 17 acres of tree-shaded bungalows and moderately priced apartments.

"This is not a decision I gladly make," said Board Chairman Stephen Detwiler, reflecting concerns that long-established neighborhoods will be affected by new housing construction along Arlington's Metro corridor.

"The more I look at that huge building, the more I think that is not the kind of housing we want to cover Arlington with," said board member Dorothy Grotos, who cast the only vote against the project.

The board in March had rejected a similar proposal by Knightsbridge, a McLean, Va., firm, saying the proposed 400-foot-long structure, which would have exceeded the area's 12-story height limit, was too tall and massive for the neighborhood.

"This is the first nail in the coffin of Colonial Terrace," said Jordan Tennenbaum, president of the local tenants association, after the vote Tuesday night.