Commerce City, Colo. ? Deer meander through fields, prairie dogs pop up from their burrows to look around, and hawks glide overhead near a site once branded the most polluted square mile in America.

The animals’ home is the 17,000-acre Rocky Mountain Arsenal, once a center of chemical weapons and pesticide production and now a federal Superfund site undergoing a $2.2 billion cleanup that will turn it into a wildlife preserve.

Federal officials are planning to designate it a national wildlife refuge in 2011, when the cleanup is expected to be completed. They envision it as a vast oasis sitting between Denver, eight miles away, and the rapidly growing suburbs to the northeast.

“It’s a great opportunity for us to have a wildlife refuge close to a large metro area. It’s a chance for people to come in contact with wild places and to preserve open space,” said Dean Rundle, the U.S. Fish and Wildlife Service manager of the refuge-in-the-making.

Some critics say transforming the site into a refuge saves the government and Shell Chemical Co. from cleaning up the land as thoroughly as they would have had to for other uses, such as homes or businesses. They claim the animals and the public are at risk.

“I certainly like the idea of wildlife refuges. I just don’t know if taking Superfund sites and making them into wildlife refuges is a wise idea,” said Sandra Horrocks of the Rocky Mountain chapter of the Sierra Club.

However, Laura Williams, the Environmental Protection Agency’s site project manager, said officials had done “more stringent cleanup in areas because of the animals. Some of these critters are more sensitive to contaminants than humans are.”

Formerly populated by farm families, the 27-square-mile site was turned into a major chemical weapons factory in 1942. Nerve and mustard gas, napalm and white phosphorous were produced during World War II. After the war, a company later acquired by Shell Chemical Co. manufactured powerful herbicides and pesticides.

When all production stopped in 1982, waste ponds full of chemical goo and trenches containing munitions and pesticide byproducts remained.

The mess prompted federal regulators to pronounce the area the “most polluted square mile in the United States” and declare it a priority under the Superfund hazardous-waste cleanup program.

Agreements struck in the mid-1990s specified that the Army and Shell would evenly split the first $500 million of the cleanup, with the Army assuming a gradually increasing share of the cost after that.

So far, $1.4 billion has been spent. Workers used a submerged incinerator to destroy 11 million gallons of hazardous waste from the ponds and demolished 200 buildings that were contaminated or deemed of no use. They are now razing 100 more structures and moving hundreds of tons of tainted dirt to hazardous-waste landfills.

The idea to turn the land into a wildlife refuge came up in 1986, when a Fish and Wildlife biologist noticed that bald eagles had taken up residence on the land for the winter. Congress approved the refuge proposal in 1992.

The more than 100 bald eagles that winter there are just one of about 300 animal species that have migrated to the mostly open land in the past four decades. The land is inhabited by about 1,000 mule deer and dozens of coyotes. The more reclusive white-tail deer can also be seen bounding through the trees.

The chemical contaminants at the site include a host of dangerous substances, some of them known or suspected carcinogens. Among the contaminants: dioxin, benzene, arsenic, mercury and toluene.

In 2000, the discovery of 10 grapefruit-sized bomblets in a restricted area, all containing deadly sarin nerve gas, led to the closing of the part of the arsenal open to the public. The area was cleaned and reopened on weekends in early November.

Some animals, particularly birds, have been found dead near contaminated sites. Several kinds of birds are monitored to determine whether toxins are moving through the food chain.