A group of western industrial and agricultural water users has begun a lobbying campaign to amend the Endangered Species Act with language that could reduce legal protection for the whooping crane, the large white bird that has become a symbol of the struggle between preservation and development.

With the Endangered Species Act up for reauthorization in Congress this year, the Colorado Water Congress, an influential combine of water suppliers and consumers, has drafted an amendment saying the act cannot override traditional western water rights.

"We'd like to think we can settle our problems through negotiations with the [federal] government," said Tom Pitts, a consultant to the Water Congress. "But if we still have problems, then we'll want to work on the act."

The specific issue behind this effort is a pair of federal rulings that blocked new water projects on the South Platte River in Colorado. Washington halted the projects because they would reduce water flow past a key whooping crane habitat hundreds of miles downstream in central Nebraska.

In a larger sense, though, the political battle reflects a collision between the pro-development ethic of century-old western water laws and the preservationist ethic reflected in the 12-year-old Endangered Species Act.

The effort by western water interests is just one element of a broad campaign by dozens of groups to insert their pet provisions into the Endangered Species Act this year. Only when the law comes up for reauthorization is any real change politically possible.

Accordingly, a coalition of industry associations, including the American Petroleum Institute, the American Mining Congress and the National Forest Products Association, has formed an "Ad Hoc Endangered Species Task Force" to follow the bill. On the other side, more than a dozen environmental groups recently held a policy session in Washington to develop their agenda for strengthening the law.

The 1973 statute established an official list of plant and animal species in danger of extinction, and committed the federal government to preserve them. There are 829 U.S. and foreign species officially listed as "endangered" today.

The law prohibits any federal or federally funded project -- a dam, a highway or even a park -- that might jeopardize an endangered species. No such project can be started until the government agency or developer obtains a "no-jeopardy" opinion from the U.S. Fish and Wildlife Service stating that no endangered species will be adversely affected.

Water interests in western states ran headlong into the act when Fish and Wildlife blocked proposed hydroelectric and irrigation projects on the Colorado River because two rare fish, the squawfish and humpback chub, might be threatened.

Then came rulings blocking two projects on the South Platte, a river that begins in the Rockies southwest of Denver and flows northeast through Nebraska.

The Fish and Wildlife Service said the Platte projects would reduce water flow downstream across wide sandbars in the river near Grand Island, Neb., where whooping cranes roost during their spring and fall migrations. Heavy spring flows are needed to flush away vegetation, the agency said, because whoopers, extremely nervous about predators, require open, unvegetated areas in which to roost.

The whooping crane, a 5-foot-tall bird of majestic mien, has become an international symbol of human efforts to save dwindling species. In 1941 there were only 15 whoopers left on Earth, the government says. The current population is believed to be 149, and prospects for survival are promising.

But the federal rulings on behalf of the whooper stunned water development interests here.

A century of court rulings and interstate agreements in this water-starved region had cleared the way for continued development of dams on western rivers -- with encouragement and funding from Washington. Suddenly, the tables were turned.

"Water law here had always encouraged development for any beneficial use," said Frank Dunkle of Fish and Wildlife's Denver office. "But fish and wildlife preservation was never considered a beneficial use. With the Endangered Species Act, it's a whole new ball game."

"The Fish and Wildlife Service has, in essence, abrogated state water allocation systems," said Pitts, the water consultant here.

The water groups have been meeting regularly with federal agencies to try to resolve their problems under the Endangered Species Act. "I thought we were starting to reach some understandings," said Dunkle, who has taken part in these sessions.

But while the water interests continue their efforts through administrative channels, they also have drafted proposed amendments to the Endangered Species Act that would effectively exclude projects on the Colorado, Platte and other rivers from that statute's dictates.

The water groups have asked westerners in Congress to sponsor their amendments when the reauthorization bill comes up. Aides to Sen. Malcolm Wallop (R-Wyo.) say he is likely to push for some such amendment in the Senate.

"The senator feels strongly that something has to be done about the western water rights issue," said Janis Budge, Wallop's press secretary. "And the bill's up for reauthorization, so now's the time to do it."

But Ann Vance, an aide to Sen. William L. Armstrong (R-Colo.), said she had urged the water interests to work for change "through regulatory or administrative channels" -- that is, by negotiating with executive branch officials -- because "this is going to be an awfully tough fight if it comes up in Congress."