Protesters drumming on orange plastic buckets and wearing white, biohazard-style coveralls rumbled down the usually quiet Sunday streets of downtown Frederick, warning that plans to create a biodefense research campus at Fort Detrick could pose a threat to residents' health.

Chanting "No more war," about 100 members of such groups as the Frederick Progressive Action Coalition, the Green Party, Women in Black, DemocracyRising.US, the Peace Resource Center of Frederick and the International Socialist Organization paraded down Market and Patrick streets yesterday afternoon, arguing against expansion.

The rally began in hot and humid conditions in the Baker Park band shell, an outdoor amphitheater. Barry Kissin, the rally's organizer, sweated it out in black clothes, a peace-symbol button on his short-sleeved shirt. He kicked off the event with a speech explaining his concerns with the government's plans.

"What's underway about two miles in this direction," Kissin said, pointing toward Fort Detrick's 800-acre Army base, "is an explosion of facilities whose function and effect will be to create a whole new generation of biological weapons and to generate a biological weapons arms race."

In an interview before the rally, Chuck Dasey, a spokesman for Fort Detrick, denied that biological weapons research is, or will be, performed there: "We don't do bioweapons. We're against bioweapons, and we're for biological arms control."

Although the two sides do not agree on the distinction between offensive and defensive biological research, it is clear that the new National Interagency Biodefense Campus will be the largest center in the United States dedicated to the study of biological agents, including smallpox and anthrax.

Congress authorized the expansion after several letters containing anthrax spores were sent to politicians and media organizations in the weeks after the Sept. 11, 2001, terrorist attacks.

"The anthrax letters showed that we did not have enough laboratory space . . . to respond appropriately to a bioterror event," Dasey said. "The campus and the facilities are the answer to that shortfall."

Fort Detrick, the city's largest employer, has 750 scientists, lab technicians and other workers from the U.S. Army Medical Research Institute of Infectious Diseases. The project would provide more space for the Army researchers and would bring scientists from the Department of Homeland Security, the National Institute of Allergy and Infectious Diseases and the Department of Agriculture onto a 200-acre campus.

Dasey said the billion-dollar expansion would add about 360 jobs at the base, which has about 7,000 workers.

The base's economic weight looms large in the mind of Frederick Mayor Jennifer P. Dougherty, who said she was "stuck between a rock and a hard place" in balancing the base's benefits with the potential danger to residents.

Her chief worry is the environmental effects of biodefense research, she said. "What is going into the air, the water and the ground?" she asked in an interview before the rally. "When will we know it is a problem? Will it be 25 years from now, when we are all suffering from illnesses that they don't know the root of?"

To minimize that risk, Dougherty wants independent air-quality testing, to warn residents if anything toxic escapes the facility. "I live six blocks away," she said. "I want to have some assurance."

Others at the rally said they were worried about being exposed to deadly biological agents.

In response to such fears, Dasey listed some security measures he said are being taken: Engineering controls regulate the airflow from the buildings. Workers are vaccinated against the agents they work with and are forbidden to work in labs alone. Access to the facilities is strictly controlled and monitored by video surveillance. Roving patrols can enter a lab at any time to ensure that workers are following safety rules.

"We think those [measures] are sufficient to allow us to say that there's no danger to the community," Dasey said.

Despite a campaign to inform the public about safety precautions, the base administration appears to have some way to go before assuaging residents' fears. Lew Cullen, a Frederick resident who took his family to a park next to the rally, said that though he was not opposed to Fort Detrick, he worried about the potential of an accident. "When's some virus they don't have a cure for going to devastate the community?" he asked.

Along the short march route, Frederick residents and tourists stopped and stared as protesters passed by, trailed by several police on bicycles.

The spectacle sparked discussion among four people enjoying margaritas at a restaurant's outdoor table. They agreed with the protesters in principle but said they wondered about the effectiveness of a noisy rally in tranquil Frederick. Sherri Robbins, a singer-songwriter who lives in the city, said she thought the message might be ignored, but she hoped the protest would stimulate debate.

"I don't think we hear enough about that side," she said of expansion opponents.

About 100 protesters from various groups chanted "No more war" as they marched against a planned biodefense site.

Some marchers in downtown Frederick wore biohazard suits and gas masks to show opposition to a new research campus at Fort Detrick.