WASHINGTON - The only U.S. facility allowed to research the highly contagious foot-and-mouth disease experienced several accidents with the feared virus, the Bush administration acknowledged Friday.

A 1978 release of the virus into cattle holding pens on Plum Island, N.Y., triggered new safety procedures. While that incident was previously known, the Homeland Security Department told a House committee there were other accidents inside the government's laboratory.

The accidents are significant because the administration is likely to move foot-and-mouth research from the remote island to one of five sites on the U.S. mainland near livestock herds. This has raised concerns about the risks of a catastrophic outbreak of the disease, which does not sicken humans but can devastate the livestock industry.

Skeptical Democratic leaders of the House Energy and Commerce Committee demanded to see internal documents from the administration that they believe highlight the risks and consequences of moving the research. The live virus has been confined to Plum Island for more than a half-century to keep it far from livestock.

The 1978 accidental release "resulted in the FMD virus in some of the cattle in holding pens outside the laboratory facility," Jay Cohen, a senior Homeland Security official, wrote in response to the committee.

"Detailed precautions were taken immediately to prevent the spread of the disease from Plum Island, and new precautionary procedures were introduced."

Cohen, undersecretary for science and technology, said there also have been "in-laboratory incidents" - contamination of foot-and-mouth virus within the facility but not outside it - at Plum Island since 1954. That was the year the Agriculture Department acquired the land and started the Plum Island Animal Disease Center.

One government report, produced last year and already provided to lawmakers by the Homeland Security Department, combined commercial satellite images and federal farm data to show the proximity to livestock herds of locations that have been considered for the new lab.

"Would an accidental laboratory release at these locations have the potential to affect nearby livestock?" asked the nine-page document. It did not directly answer the question.

A simulated outbreak of the disease in 2002 - part of an earlier U.S. government exercise called "Crimson Sky" - ended with fictional riots in the streets after the simulation's National Guardsmen were ordered to kill tens of millions of farm animals, so many that troops ran out of bullets. In the exercise, the government said it would have been forced to dig a ditch in Kansas 25 miles long to bury carcasses. In the simulation, protests broke out in some cities amid food shortages.

"It was a mess," said Sen. Pat Roberts, R-Kan., who portrayed the president in that 2002 exercise. Now, like other lawmakers from the states under consideration, Roberts supports moving the government's new lab to his state. Manhattan, Kan., is one of five mainland locations under consideration. "It will mean jobs" and spur research and development, he says.

Other possible locations for the new National Bio- and Agro-Defense Facility are Athens, Ga.; Butner, N.C.; San Antonio; and Flora, Miss. The new site could be selected later this year, and the lab would open by 2014. The number of livestock in the counties and surrounding areas of the finalists range from 542,507 in Kansas to 132,900 in Georgia, according to the Homeland Security Department's internal study.

Foot-and-mouth virus can be carried on a worker's breath or clothes, or vehicles leaving a lab, and is so contagious it has been confined to Plum Island since the research began. The existing lab is 100 miles northeast of New York City in the Long Island Sound. Researchers there who work with the live virus are not permitted to own animals at home that would be susceptible, and they must wait at least one week after work before attending outside events where such animals might perform, such as a circus.

Leaders of the House Energy and Commerce Committee also are worried about the lab's likely move to the mainland. Chairman John Dingell, D-Mich., and the head of the investigations subcommittee, Rep. Bart Stupak, D-Mich., also demanded reports about "Crimson Sky" and other studies on the consequences of live virus research on the U.S. mainland. Cohen, the Homeland Security official, said those documents were provided.

Two lawmakers from New York, Sen. Hillary Rodham Clinton and Rep. Timothy Bishop, both Democrats, expressed concerns in letters they wrote last year about the Homeland Security Department's ability to protect the existing lab at Plum Island, which relies for security on a private security company and local police rather than federal agents.

"We are particularly concerned that DHS has not been meeting the security needs of the facility since Federal Protective Service agents were removed from the island," Clinton and Bishop wrote in a letter obtained by The Associated Press.

Cohen responded that Plum Island used a contract with a private security firm and relied on an agreement with local police, who were deputized to enforce federal laws on the island.

Will Jenkins, Bishop's spokesman, said Friday that Homeland Security "has been responsive to the concerns raised last year, and Congressman Bishop is pleased with the progress DHS is making regarding security for Plum Island."

The White House said modern safety rules at labs are sufficient to avoid any outbreak. But incidents in Britain have demonstrated that the foot-and-mouth virus can cause remarkable economic havoc - and that the virus can escape from a facility.

An epidemic in 2001 devastated Britain's livestock industry, as the government slaughtered 6 million sheep, cows and pigs. Last year, in a less serious outbreak, Britain's health and safety agency concluded the virus probably escaped from a site shared by a government research center and a vaccine maker. Other outbreaks have occurred in Taiwan in 1997 and China last year and in 2006.

If even a single cow signals an outbreak in the U.S., emergency plans permit the government to shut down all exports and movement of livestock. Herds would be quarantined, and a controlled slaughter could be started to stop the disease from spreading.

Infected animals weaken and lose weight. Milk cows don't produce milk. They remain highly infectious, even if they survive the virus.

The Homeland Security Department is convinced it can safely operate the lab on the mainland, saying containment procedures at high-security labs have improved. The livestock industry is divided. Some experts, including the former director at the aging Plum Island lab, say research ought to be kept away from cattle populations - and, ideally placed where the public already has accepted dangerous research.

The former director, Dr. Roger Breeze, suggested the facility could be safely located at the Atlanta campus of the Centers for Disease Control and Prevention, or at Fort Detrick in Frederick, Md., home of The United States Army Medical Research Institute for infectious diseases.

Another possibility, Breeze said, is on Long Island, where there is no commercial livestock industry. That would allow retention of most of the current Plum Island employees.

The former head of the Agriculture Department's Agricultural Research Service said Americans are not prepared for a foot-and-mouth outbreak that has been avoided on the mainland since 1929.

"The horrific prospect of exterminating potentially millions of animals is not something this country's ready for," said Dr. Floyd Horn.

The Agriculture Department ran the Plum Island lab until 2003. It was turned over to the Homeland Security Department because preventing an outbreak is now part of the nation's biological defense program.

Plum Island researchers work on detecting the disease, controlling epidemics using vaccines and drugs, testing imported animals and training professionals.

The new facility will add research on diseases that can be transferred from animals to humans. The Plum Island facility is not secure enough to handle that higher-level research.

A new facility at Plum Island is technically a possibility. Signs point to a mainland site, however, after the administration spent considerable time and money scouting new locations. Also, there are financial concerns about operating from a location accessible only by ferry or helicopter.

The Homeland Security Department said laboratory animals would not be corralled outside the new facility, and they would not come into contact with local livestock. All work with the virus and lab waste would be handled securely and any material leaving would be treated and monitored to ensure it was sterilized.

"Containment technology has improved dramatically since foot-and-mouth disease prohibitions were put in place in 1948," said Homeland Security spokeswoman Amy Kudwa.

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Associated Press writer Sharon Theimer contributed to this report.