In another federal attempt to guard the Washington skyline, the Interior Department has challenged a zoning ruling in a move to force Arlington officials to reconsider their approval of a proposed 29-story Rosslyn office and hotel complex.

In a 12-page memorandum personally approved by Interior Secretary Cecil D. Andrus, the department is asking Arlington's Board of Zoning Appeals to overturn a decision by Zoning Administrator Van Caffo on the grounds that he prematurely certified that construction of the high-rise project was under way.

Under normal zoning procedure, once construction has begun the Arlington County Board cannot reconsider its earlier approval of a project.

"We don't believe that digging a little strip of ground is construction under Virginia law," said assistant Interior Department solicitor Rick Robbins yesterday.

On Feb. 8, one day before county approval of the Arland Towers building plans would have expired, developer Stanley Westreich was granted an excavation permit and crews began bulldozing a strip of land at 1101 Wilson Blvd., the site of the proposed complex.

Arlington officials and Westreich said yesterday they found the federal challenge to Caffo's ruling baffling and "absurd."

"For them to say that digging a hole in the ground isn't starting construction is unreasonable," Caffo said.

"We think this is very strange," said developer Westreich.

If the project's building plans had expired before the excavation permit was granted, Westreich would have had to come back last month before the County Board in a public hearing and request reapproval for the controversial project.

That hearing would have occured at the same time Justice Department lawyers were asking federal Judge Oren R. Lewis to rule that several Rosslyn buildings be scaled down because they will constitute a public nuisance and will spoil the Washington skyline.

Lewis ruled that the high-rise buildings, which will be the tallest in the Washington area, would not deface the skyline surrounding the national monuments.

Justice and Interior attorneys are preparing to appeal Lewis' ruling to the 4th U.S. Circuit Court of Appeals.

In papers filed with the County Board of Zoning Appeals, the Interior Department claims that excavation merely represents work preparatory to construction and not construction itself.

"The determination by the zoning administrator that the scraping upon a portion of a site amounts to the construction of the office tower is without factual or legal basis," the papers say. "The activity of the Arland Towers Co. [represents] preliminary work incidental only to commencement of construction."

In addition, the papers note, because neither demolition nor building permits had been issued as of March 8, construction had not actually begun. County officials said that a demolition permit was issued yesterday.

Robbins said that should the fivemember board rule against the Interior Department at its hearing scheduled for May 7, the department could appeal the ruling to the Arlington Circuit Court.

"We're just not going to let any opportunity [to challenge the buildings] slide by," he said.