The high-rise urban hub and professional basketball arena proposed for downtown Brooklyn’s Atlantic Yards would be vulnerable to a devastating terrorist attack because of design flaws in architect Frank Gehry’s plans for the site, according to a recent report co-authored by a Defense Department analyst that was released to The New York Sun.

The arena is at the heart of real estate mogul Bruce Ratner’s bid for downtown Brooklyn’s 8.5-acre rail yard, which is currently owned by the Metropolitan Transportation Authority. Mr. Ratner’s firm, Forest City Ratner, commissioned Mr. Gehry, an acclaimed architect best known for his work on the Guggenheim Museum in Bilbao, Spain, to design the arena and the surrounding high-rises.

The 10-page “white paper” examining the Gehry plan was written over a three-month span by a senior environmental analyst at the Defense Department, Christina Cope, and a retired MTA strategic analyst, Alan Rosner. Ms. Cope’s prior work includes several Army range modernization projects, including live-fire training facilities. In an interview with the Sun, Ms. Cope said that she takes no stance on the bidding war over the Atlantic Yards site that pits Mr. Ratner’s firm against Extell Development Company, which has offered the MTA an undisclosed sum for the rail yard.

The report recommends changes to the planned glass exterior of the sports arena. According to the authors, an estimated 80% of all casualties from terrorist attacks result from breaking glass. The report also charges that the sports arena and the towers slated for the Atlantic Yards site would not be set back sufficiently from the surrounding streets, “making them subject to the full force of car or truck bombs.” Similar concerns prompted the redesign of the Freedom Tower planned for Ground Zero.

Ms. Cope and Mr. Rosner completed their white paper early this month and presented it to a group formed in opposition to the Ratner plan, Develop Don’t Destroy. A spokesman for the group, Daniel Goldstein, vehemently denied a report in a local weekly, Brooklyn Papers, which claimed that Develop Don’t Destroy had commissioned Ms. Cope and Mr. Rosner to compose the document. But Mr. Goldstein said he has distributed the white paper to about four dozen public officials, including the police commissioner, Raymond Kelly.

In a phone interview with the Sun, Ms. Cope said that Mr. Gehry’s plan does not provide for a large open space to which fans could flee in the event that the arena were to be evacuated. She said that the combined effect of residents and office-workers leaving the high-rise buildings, fans exiting the arena, and commuters emerging from the transit hub below would make the site particularly vulnerable to a deadly stampede. Ms. Cope said that the concerns expressed in her report are unique to the Ratner plan and could not necessarily be cross-applied to other sports arenas situated on top of transit hubs. For example, she said, Madison Square Garden is mostly surrounded by wide four-lane streets and pedestrian walkways, facilitating safe exit routes in an emergency.

The authors also charge that Mr. Gehry’s plan for 19 buildings around a central courtyard would allow a lone terrorist driving an explosive-laden truck to destroy several skyscrapers with a single blast. Ms. Cope suggested that Mr. Gehry should add concrete barriers to the courtyard entrances.

“A large truck or van could still knock down a concrete barrier, but they would need to pick up a lot of speed,” she said. Ms. Cope also said that Atlantic Yards planners could reduce the risk of an attack by placing bomb-sniffing dogs, police patrols, and surveillance cameras at entry points to the courtyard.

“Unfortunately, once these security measures are implemented, the complex will become a fortress-like superblock,” according to the report. That could negate some of the economic benefits that promoters of the Ratner plan have said the project would bring to the surrounding community.

A spokeswoman for Forest City Ratner, Lupe Todd, said that the firm had no comment on the white paper. Spokespeople for Mr. Kelly and the Brooklyn borough president, Marty Markowitz, could not confirm that either official had read or even received the report. A mayoral spokeswoman said that Mr. Bloomberg had not received the report.