The Arlington County Board yesterday approved a proposal by the Charles E. Smith Co. to build a $50 million, 900-unit Marriott Hotel in a three-block area of Crystal City between Rte. 1 and South Eads Street.

The 16-story twin-tower convention hotel - triple the size of any in Arlington and the eighth major hotel in Crystal City - will be located across the street from an existing 340-room Marriott Hotel.

"Marriott has an outstanding occupany rate and this hotel is an outstanding opportunity for us and for the county," the Smith Company attorney, Barnes Lawson, told the board. According to Lawson, the hotel will generate an estimated $1.5 million annually in local tax revenue.

In other action, the board approved a plan by the nonprofit Alcoholic Rehabilitation Inc., to buy a small garden apartment building and operate it as a dormitory for 52 recovering alcoholics and staff members.

"The people were normal everyday citizens at one time, living in this community, who go to work one week after they come here," said the facility's director, Dr. Joseph Kline.Kline urged the board to grant a license for the dormitory to be located at 506 N. Pollard St.

Several area residents, including some of the 40 tenants who would be forced to leave the moderate-rent complex near the Parkington Shopping Center, opposed the licensing and sale of the building by the Arledge Realty Co.

Some tenants said that while they supported the idea of a halfway house, they resented being forced onto Arlington's already crowded rental housing market. But county board members told the tenants that Arledge officials have offered to relocate residents in nearby moderate rental apartment buildings that the firm manages.

"This facility will be degrading to the neighborhood and no member of this board would vote for it in his community," one resident angrily told board members.

"This is my neighborhood," Board Chairman Dorothy T. Grotos countered. "It's very unfortunate that we're displacing people but those who are coming in are also low income, so we're really providing housing."