the Arlington County Board rebuffed yesterday federal objections to two controversial high-rise projects in Rosslyn and Crystal City.

In separate actions, the board turned aside a request to revoke a recently-issued excavation permit for a 29-story building in Rosslyn and approved a 20-story high-rise hotel near National Airport.

In the Rosslyn action the board declined to act on a request by John Parsons, associate regional director of the National Park Service, to revoke a permit issued Wednesday to Arland Towers, one of four Rssslyn high-rise buildings now the subject of a lawsuit pending in federal court.

That suit was filed at the request of Interior Secretary Cecil D. Andrus, who called the buildings "monsters" and said they would "visually deface the skyline surrounding the national monuments."

Following Parsons' request, board chairman Dorothy T. Grotos asked County Attorney Jerry K. Emrich if approval of the permit can be rescided. "Virginia law is very clear that the board can't change its mind" after approving a project, Emrich said.

After debate involving many of the issues that have made Rosslyn so controversial, the board approved a 20-story Hyatt hotel to be located in the 3100 block of Jefferson Davis Highway (Rte. 1), south of Federal officials including Parsons, and several area residents had objected to the hotel, to be developed by Kingdon Gould.

"We're talking about creeping building height," said Parsons, who told the five-member board that the hotel -- four stories above Arlington's height limit -- would constitute a "visual imposition from the George Washington Parkway and Hains Point."

Gould's attorney, Martin D. Walsh, told the board that the hotel would generate about $1 million dollars annually in tax revenue and that Gould had agreed to pay for the construction of roads and sidewalks in the area.

These reasons often have been cited by Arlington officials as justification for approval of tall buildings such as Arland Towers in Rosslyn.

"Arlington County has tried to do things on the cheap, to get developers to provide roads and sidewalks and then we don't like what we get," said citizen activist Louise Chestnut, who angrily urged the board to reduce the height of the hotel.

Board member Ellen M. Bozman who voted with john W. Purdy against the totel said she would rather have Arlington County pay for roads than grant increased heitht.

Grotos, vice chairman Walter L. Frankland Jr., and newly-installed board member Stephen H. Detwiler voted for the hotel.