The Supreme Court announced yesterday that it will decide how extensively government can regulate the nation's wetlands, a key source of contention among environmentalists and property owners.

Property owners in two cases the court agreed to hear argue that government regulators have interpreted the 1972 Clean Water Act too broadly and exceeded their power to regulate interstate commerce, because the wetlands in dispute are miles from any waters able to support recreation or shipping.

In accepting the cases, the court ruled against the Bush administration, which had said in a brief that "core federal interests" were at stake and urged the court to let stand lower-court rulings that upheld the government's authority.

The case could present an early test of new Chief Justice John G. Roberts Jr.'s thinking on the scope of Congress's power under the commerce clause, a question mark left from his confirmation hearings.

At that time, Roberts's opponents cited an opinion he wrote as a federal appeals judge and suggested that he was skeptical of federal environmental regulations that were justified by the wider repercussions of local development. But the opinion was a brief dissent that did not offer a definitive view on the matter.

At the center of the debate is the Clean Water Act, which gave the federal government authority to block pollution in "the waters of the United States." At the time, this jurisdiction was premised on Congress's power to regulate interstate commerce on the country's "navigable" waters.

Since then, federal regulators have defined the waters of the United States to include wetlands that are "adjacent" to larger rivers or lakes, but there is dispute about the precise meaning of "adjacent."

The government views wetlands as part of complex ecosystems that must be kept clean to preserve the quality of the larger bodies of water they ultimately feed. Property owners, supported by such organizations as the National Association of Home Builders, say this is a sweeping definition that rubs out state and local land-use authority -- and adds to the cost of housing.

The court tried to avoid the constitutional issue in 2001, when it ruled that the federal government could not use the Clean Water Act to protect small, shallow ponds in Illinois just because they are used by migratory birds.

In that case, the court implied that the Clean Water Act required a "significant nexus" between a wetland and an "adjacent" larger body of water.

But, as subsequent rulings by lower courts have shown, that left open a deeper question of whether it is enough for a wetland to be part of the same large hydrological system as a river or lake, or whether the wetland must directly abut the larger body.

Both cases accepted by the court yesterday are from the Cincinnati-based U.S. Court of Appeals for the 6th Circuit, which has advocated a broad view of the Clean Water Act's coverage.

In the first case, Carabell v. U.S. Army Corps of Engineers, No. 04-1384, Michigan property owners were denied permission to build a condominium complex in Macomb County, Mich., outside Detroit. The Corps of Engineers said that, although the property is separated by a berm from a ditch that feeds water into Lake St. Clair, it is nonetheless "adjacent" to the ditch and thus to "waters of the United States."

In the second of the cases, Rapanos v. United States, 04-1034, a Michigan man who wants to develop shopping centers faces steep civil and criminal penalties for filling in wetlands on three sites, despite repeated government prohibitions.

Oral arguments will take place in early 2006, and a decision is expected by July.