CHICAGO — Federal officials on Wednesday ordered Dow Chemical to clean up high levels of dioxin recently discovered in the homes and yards of a Saginaw, Mich., neighborhood downstream from the company's world headquarters.

Preliminary results from tests conducted in March by the U.S. Environmental Protection Agency found dioxin levels in household dust and outdoor soil that were well above the federal cleanup standard. The amount in a sample taken from one yard was 23 times higher than what the EPA considers reasonably safe.

The new order is a result of aggressive action taken against Dow by the EPA's former top official in the Midwest, Mary Gade, who told the Tribune last month that the Bush administration forced her out as head of the agency's Chicago-based office over heated disputes between the chemical company and environmental regulators.

It marks the first time that federal officials have forced a dioxin cleanup in a residential area near Dow's sprawling Midland, Mich., chemical plant. The EPA issued four similar orders last year, three for industrial areas and another along a public park.

Before Gade stepped in, cleanup had been minimal. The most extensive work, negotiated by the state, had involved scouring the interiors of 300 homes and spreading wood chips over contaminated soil outside.

Earlier this year, Gade surprised Dow officials and local residents when she ordered new tests in residential areas downstream from the company's plant. The results disclosed Wednesday revealed high dioxin levels in and around a stretch of homes about 20 miles from the plant, near where the Tittabawassee and Saginaw Rivers meet.

One sample of household dust had dioxin levels of 3,000 parts per trillion, three times more than the federal cleanup standard. Levels in the yards were as high as 23,000 parts per trillion and averaged 2,000 parts per trillion.

"This highlights why it is so important for the agencies to keep holding Dow accountable for its actions," Gade said Wednesday in a brief interview.

For most of the past century, the company dumped dioxin-laden waste into rivers that stretch for 50 miles into Saginaw Bay and Lake Huron. But efforts to clean up the area have been delayed by decades of legal wrangling by Dow, which for years insisted it wasn't responsible.

The company still contends dioxin-contaminated soil and sediment doesn't threaten people or wildlife. At the same time, it says it is prepared to restore polluted areas but disagrees with state and federal officials about how the massive project should be carried out.

"We've said all along that if there are things that need immediate attention, we are prepared to deal with that," said spokesman John Musser.

Dioxin was a manufacturing byproduct of the herbicide Agent Orange and other chemicals manufactured by Dow. The EPA says it causes cancer and disrupts the immune and reproductive systems, even at very low levels.

Federal and state officials met with Dow executives on Wednesday to discuss how the cleanup will proceed.

"We want rapid action in that neighborhood to minimize potential exposure," said Ralph Dollhopf, associate director of the EPA's regional Superfund office.

Some of the homes involved were part of the previous scouring efforts, said Robert McCann, spokesman for the Michigan Department of Environmental Quality. "That obviously wasn't enough to take care of the problem."