The Smithsonian Institution revealed yesterday that stopping work on the undulating glass canopy planned for the Old Patent Office Building -- which it was forced to do by the National Capital Planning Commission last week -- will cost an estimated $8 million.

Last week's 6 to 5 "no" vote by the commission came as a surprise because the same group had voted twice last year to approve the project. In July, the design concept won an 8 to 4 vote in its favor. In November, the vote was 8 to 3 in support of preliminary designs by Foster and Partners, the London firm headed by Lord Norman Foster.

Given these approvals, said Smithsonian spokeswoman Linda St. Thomas, both the architect and the contractors moved ahead with the plan to roof over the courtyard of the historic building, which houses two Smithsonian museums -- the National Portrait Gallery and the American Art Museum.

Stopping work on such a major construction project isn't as simple as stowing a shovel back in the old toolshed. Moving all the heavy equipment and construction trailers, storing materials that already have been bought and, in general, "demobilizing" the site actually takes a lot of work.

And costs money. The Smithsonian came up with the $8 million estimate in collaboration with Hensel Phelps Construction, the prime contractor on the project. The sum includes payments already made to contractors, architects and fabricators as well as certain penalty fees written into construction contracts, St. Thomas said.

Some part of the $8 million loss could be recovered, St. Thomas said, should the Smithsonian get quick approval of a revised design. Such a design, including a glass canopy, may be submitted to the commission as early as August or September, she said.

Planning Commission Chairman John V. Cogbill said he had been "in direct contact with some of the senior Smithsonian leadership trying to move this forward." The commission, he said, "wants to find a resolution that works for the standards of those most strenuous advocates for the iconic and historic aspects of this building, and blend that with what is new and exciting."

As part of its negative vote, the commission recommended that the Smithsonian "reconstruct the courtyard in a manner that will rehabilitate its prior design character." The formerly grassy courtyard has been open to the sky since the building's completion in 1867. However, the commission did not completely rule out a "revised design for enclosing the courtyard."

It is certain that, covered or uncovered, the new courtyard will contain the two cast-iron fountains that were removed when excavation for a new subterranean auditorium was begun.

The commission last week ordered that they be reinstalled, and the Smithsonian, said St. Thomas, has stored the fountains and is prepared to rehabilitate them. But as for the auditorium now under construction beneath the courtyard, St. Thomas said, its roof will not be strong enough to support soil and grass.

The building has been closed for five years for extensive renovations, and is scheduled to reopen July 4, 2006. The $166 million renovation is covered by a congressional appropriation, but the courtyard project is to be privately financed.

The usual estimate has been $40 million to $50 million, $25 million of which was donated last year by Washington art collectors Robert and Arlene Kogod.

A rendering of Norman Foster's proposed -- and rejected -- courtyard enclosure of the Old Patent Office Building.