Twenty years ago, it took an act of Congress before the Tennessee Valley Authority could proceed building the Tellico Dam. The reason: Advocates of saving the snail darter, a tiny fish suspected of being nearly extinct, convinced the U.S. Supreme Court that the fish's fate counted more than the $137 million construction project.

In the 1970s, the Endangered Species Act was used to halt development and protect habitats of species on the brink of oblivion. Today, the government is enforcing the law in more productive and inventive ways.

Businesses and industries routinely work with federal officials on plans and arrangements to protect vast numbers of species while pursuing development of sensitive habitat areas. Landowners and enforcement officials are creating management plans on private property that serve the law's objectives but still allow development.

The Endangered Species Act no longer simply protects one imperiled species after another. The law now is seen as a way to protect healthy biological diversity. But without private landowners' participation, the law won't accomplish its goal. That's why Congress and the Interior Department are looking for ways to give developers a bigger role in protecting biological diversity.

Five years ago, business groups waged war on the Endangered Species Act. As a compromise - essentially to save the Act from major gutting or outright repeal - the Clinton Administration began to promote the use of "habitat conservation plans" (HCPs) on private lands.

HCPs are voluntary agreements whereby a landowner adopts conservation measures, which sometimes are stricter than what the law requires, and the government approves the development of property that harms endangered wildlife and habitats.

Under an HCP, for example, federal officials would agree not to oppose a landfill expansion in exchange for the site owner's commitment to leave some vegetation untouched to protect wetlands from sediment and stream banks from erosion, and to preserve other natural features.

Congress first authorized HCPs about 15 years ago, but very few were consummated until 1994. Over the past couple of years, however, more than 200 plans have been negotiated and hundreds more are in the works.

Still, the new approach is not universally well-received. Some environmentalists and wildlife biologists are wary, if not downright antagonistic.

"Under many HCPs, development is permitted and habitat is destroyed despite great uncertainty about whether the landowners have provided enough mitigation to sustain species in the long run," says a report issued by the Defenders of Wildlife, a Washington, D.C.-based environmental group.

Skeptics and critics particularly are disturbed by a feature of the plans that property owners consider to be crucial: the no-surprise clause. Under this provision, the government promises not to add new restrictions on how the land is used during the plan's term, which can be 25 years or longer. In the meantime, the landowner's activities may harm some of the species or habitat, but such "incidental takings" are expressly permitted.

The government's promise endures, even if unforeseen circumstances arise, which might otherwise require different or additional measures to preserve species or habitat. However, if the landowner consents, then additional preservation steps can be imposed at the government's expense.

"Landowners ... have a legitimate concern," says Secretary of the Interior Bruce Babbitt. "They want some assurance that once they agree to be a party to an HCP and to mitigate the effects of their activities on listed species, we won't come back later for a second bite from the apple. A deal is a deal."

Bipartisan Senate supporters of the no-surprise policy would like to see it expressly incorporated into the Act itself, and the Administration supports such an effort. However, sponsors of a pending bill have been unable to bring it to the U.S. Senate floor.

Considerable disagreement exists over how to pay the government's costs when nature, which is full of surprises, acts in its own way while no-surprise clauses force the government to pay landowners. The bill's supporters have proposed to pay these costs by auctioning federal land tracts.

As expected, conservation advocates are irate. Environmental groups favor a measure that was introduced in the U.S. House by Rep. George Miller, D-Calif. Overall, the chances are slim for changing the law before Congress adjourns for the November elections.