The Arlington County Board yesterday approved a developer's proposal to build twin 19-story luxury condominium towers along Rte. 1 north of Crystal City instead of a previously approved 11-story apartment building.

The board's decision gives the Charles E. Smith Co., the major developer of the nearby Crystal City complex, enough additional height to add 82 condominium units to be priced at $100,000 each, to a $100 million 16-acre project known as Jefferson Plaza.

Located south of the Pentagon along Jefferson Davis Highway, Jefferson Plaza is planned as a seven-building high-rise office and residential development to be completed in 1984.

Smith Co. attorney Barnes Lawson told the board that he was requesting the height increase because it would permit a change in the design of the building. "In exchange," Lawson said, "we are offering a much more attractive plan" that would be better landscaped.

In return for height which exceeds Arlington's zoning limit by three stories, Lawson said that Smith Co. would provide "a community amenity" in the form of an underground tunnel linking Jefferson Plaza with Smith's other buildings in Crystal City and the Metro station there.

"We don't see what more a developer could be asked to do," said Robert Smith, the firm's vice president. "We are a one-company crusade to bring people to Arlington."

Several Arlington residents spoke in opposition to the increased height, but all four county board members present yesterday approved the change.

"This amenity is going to be very good for (Smith)," said Louise Chestnut, a citizen activist. "I hear tradeoffs, but I don't see that we're getting very much in return as a county. Heights in Arlington seem to be like yeast in bread: they go up but they never come down."

During a recent hearing before the county planning commission, an official for the National Capital Planning Commission said he did not oppose Smith's request but warned of "creeping building heights in the Jefferson Davis corridor." Several federal agencies have bitterly contested recent highrise projects in the county, which they say may mar the Washington skyline.

Although county board member Ellen M. Bozman initially questioned quest for additional height on the Smith building, she joined the other board members in voting to grant Smith's request. Board chairman Dorothy T. Grotos was absent yesterday.