The Arlington County Board yesterday turned aside an extraordinary request from four federal agencies that construction be stopped on several new high-rise buildings designed to tower above the present skyline in Rosslyn.

"We are very deeply concerned about the serious threat to the appearance of Washington," Charles Atherton of the federal Commission on Fine Arts told the County Board.

"Today, you look out from the Kenedy Center terrace and just see the tops" of the existing high-rise buildings in Rosslyn, Atherton said as board member were shown slides of the view of Rosslyn from the Washington side of the Potomac River. "But when you get to 357 to 380 feet (above the river level), you can see the change that's to take place.'

New buildings approved by the County Board within the last two years for Rosslyn will rise to 22, 24, and 29 stores each and up to 380 feet above the Potomac. The tallest will be the twin Arland Towers, a 29-story office and hotel complex to be built on the hillside above the river near the center of Rosslyn.

The tallest building now standing in Rosslyn - where high-rise hotels, office and apartment buildings have replaced pawnshops, lumber yards and honky-tonk bars in the last 18 years - is 15 stories high.

Across the river in Washington, buildings have been limited to 13 stories, or 130 feet. However, a special exception was made recently for redevelopment along Pennsylvania Avenue between the Capitol and the White House, where some buildings up to 16 storeis, or 160 feet, will be permitted.

Joining Atherton of the Fine Arts Commission in the appearance before the County Board yesterday were officials from the National park Service, the General Services Administration and the National Capital Planning Commission.

County Board members answered them by saying, in effect, that it is unlikely they will reconsider their approval of the taller new buildings. They did indicate their willingness to attend meetings between the federal officials and the buildings' developers who would be free to modify their designs if they wish.

John Parsons, associate regional director of the National Park Service, noting that two million people visit the Iwo Jima Memorial adjacent to Rosslyn each year, said an existing apartment house and a planned luxury condominium building "violate the green sheath buffer of trees which once lay like a ribbon along the Potomac River."

GSA regional administrator Walter V. Kallaur suggested that the federal government, a major tenant of Rosslyn, may not need much more space there."In the 1980s the enormous appetite of the federal government will not be there," he said.

County Board member Dorothy T. Grotes asked County Attorney Jerry K. Emrich whether the baord could reconsider approval of the buildings.

"The board would have to conclude that it made a huge mistake or that circumstances have changed," Emrich said. "I just don't think it would fly" because Virginia courts traditionally have ruled against such reconsiderations.

Board member Joseph S. Wholey noted that current Rosslyn zoning law requires that developers "convince the board that [additional height] is in the public interest." In the case of at least two of the new buildings, approval was granted in exchange for substantial street improvements and donations of parkland by the developers.

Two weeks ago the County Board approved a 13-story office building on the last remaining tract of land in Rosslyn, a project that county planners say will complete the area.