The Smithsonian Institution returned yesterday to the National Capital Planning Commission with design alternatives for the glass canopy planned for the Old Patent Office Building. In two versions the trademark curves of architect Norman Foster have disappeared.

Eight weeks ago, the commission rejected the prize-winning British architect's innovative design, siding with critics who thought the covering was too high and too bright, and at odds with the 19th-century landmark. The Smithsonian had decided to add a glass roof that would connect the interior walls of the building and enclose a courtyard. Yesterday's session at the commission office was an informational meeting, with the options detailed in computerized sketches and colorful diagrams.

Sheila Burke, the museum's deputy secretary and chief operating officer, said the Smithsonian plans to submit a package to the commission today with a canopy design, a landscape concept with a water element, restoration of an exterior staircase that was demolished in the 1930s and incorporation of antique fountains that had been removed from the courtyard. "It has been a challenging balancing act," she told the panel. "We take the stewardship of the building very seriously."

The commission has scheduled a vote for Sept. 8.

Burke warned that two of the five alternatives presented yesterday were radical and extremely costly departures from the original concept. If the Smithsonian submitted for approval the design with a flat roof and repositioned columns in the courtyard, the entire courtyard would have to be dug up again. That concept would raise the cost, said Burke, from the previous $47 million to more than $90 million. It also would delay the reopening of the entire building at Ninth and G streets NW for at least a year after the scheduled July 2006 date, and the installation of the enclosure.

"For a variety of reasons, we don't favor those options. We couldn't open the building on time, and there's the dramatic increase in cost. And if you move the columns you impact on the appearance of the interior space," Burke said. In addition, the flat roof would reduce the light into the courtyard by anywhere from 25 to 50 percent. The landscaping plan by designer Kathryn Gustafson would suffer from the diminished light.

The design team, including members of Foster's London office, described three other options that retained the glass canopy but lowered it by 111/2feet. The canopy would be supported by steel beams. Those plans would maintain the signature curvature of Foster's design but hide the pediment of the roof from public view. NCPC members had raised questions about the interior landscaping and the visibility of the roof in downtown Washington. The designers said the roof could be seen from 800 to 1,200 feet in two directions.

Whatever design -- or perhaps hybrid design -- is selected would use a low-iron glass with no tint to provide more clarity and would redirect all interior lights so the roof would not have a beacon effect. Those were concerns of the commission.

"The glass is a very thoughtful change," said John Cogbill III, the NCPC chairman. "They have obviously spent a lot of time deciding what the options are."

Before the June rejection, the panel on two occasions had approved a concept and preliminary design. The Smithsonian has estimated it cost $8 million to stop the work.

Criticism of the design by historic preservation groups was a key element in the commission's reversal. Four influential groups, including the Interior Department, the federal Advisory Council on Historic Preservation and the National Trust for Historic Preservation, had problems with the approach, saying the canopy would spoil the historic character of the building. That the Smithsonian destroyed the 19th-century courtyard and dug up some historic trees during the renovation angered the preservationists.

The landmark Patent Office Building, principally designed in the 1830s, has been closed since 2000. It is home to two Smithsonian art museums, the National Portrait Gallery and the Smithsonian American Art Museum, which attracted slightly fewer than 450,000 people a year before the renovation work began.

The canopy project has received congressional approval, but private contributors are footing the bill. Congress did provide $166 million for the restoration and modernization of the two museums.

Three of the five alternative plans, including this one, would retain Norman Foster's wavy glass canopy.