WASHINGTON – The Supreme Court ruled yesterday that the government can block development on hundreds of millions of acres of wetlands, even on land miles away from waterways, as long as regulators prove a connection to the waterways.

Chief Justice Roberts, in his first major environmental case, came up one vote short of dramatically limiting the scope of the landmark Clean Water Act.

At the same time, property rights advocates won a small victory with a new test, authored by moderate Justice Kennedy, for determining what land can be regulated.

Virtually any land in America would be covered under the government’s interpretation of the law, Justice Roberts and the court’s other three conservatives complained in an opinion.

The court’s four liberal members said the conservatives would have opened up sensitive wetlands to polluters.

It was a dramatic conclusion to a pair of property rights cases the justices agreed to review last fall, just days after Justice Roberts joined the court. The Bush administration defended the law and had urged the court to stay out of the case.

The justices were so splintered that there were five separate opinions covering 100 pages. The key decision was by Justice Kennedy, who agreed with the liberal members that federal regulations can apply to land adjacent to tributaries, including tributaries that are not filled with water all year.

Justice Kennedy, however, joined conservatives in ruling that regulators may have misinterpreted the Clean Water Act when they refused to let two Michigan property owners build a shopping mall and condominiums on wetlands they own.

The justices voided rulings against Keith Carabell and John Rapanos. Mr. Carabell wanted to build condos on wetlands on property about a mile from Lake St. Clair in Macomb County, Mich. Mr. Rapanos filled in wetlands near Midland, Mich., on property that is about 20 miles from a river that empties into Lake Huron. Mr. Rapanos was prosecuted by the federal government and faced a separate civil lawsuit.

“The court is clearly troubled by the federal government’s view that it can regulate every pond, puddle and ditch in our country,” a Pacific Legal Foundation attorney who represented Mr. Rapanos, Reed Hopper, said.

Environmental groups were relieved the ruling was not sweeping.

“Five justices of the Supreme Court wrote or joined opinions that support broad protection for rivers, streams, and wetlands under the Clean Water Act,” the executive director of the Community Rights Counsel, Doug Kendall, said.

Jim Murphy, a lawyer with the National Wildlife Federation, said: “Justice Kennedy saves it from being an absolute disaster.”

Justices seemed worried about the impact of the ruling.

Justice Roberts said the result was confusing and that “lower courts and regulated entities will now have to feel their way on a case-by-case basis.”

Justice Stevens, the leader of the court liberals, said Congress or the Army Corps of Engineers – and not appointed judges – should clarify the issue.

He predicted developers will be confused about whether they must get permits to do work, and federal regulators will struggle to apply a test spelled out by Justice Kennedy to determine whether land has a connection to a navigable waterway.

Justice Kennedy said the wetlands must “significantly affect the chemical, physical, and biological integrity” of nearby navigable waters to come under the Clean Water Act.

“There’s going to be a lot of administrative headaches,” an attorney with Environmental Defense, Timothy Searchinger, said. “Ultimately every water body that’s protected today should still be protected.”

Justice Scalia led the conservative bloc, including Justice Roberts, Justice Thomas, and Justice Alito. Justice Scalia said federal regulators contend they have jurisdiction over as much as 300 million acres of swampy lands in America, “including half of Alaska and an area the size of California in the lower 48 states.”

“The entire land area of the United States lies in some drainage basin,” he wrote. Justice Scalia had said the Corps of Engineers misinterpreted the term “waters of the United States.”

“In applying the definition to ‘ephemeral streams,’ ‘wet meadows,’ storm sewers and culverts, … man-made drainage ditches, and dry arroyos in the middle of the desert, the Corps has stretched the term ‘waters of the United States’ beyond parody,” he wrote.