But Corps Brig. Gen. William Grisoli said, "I'm confident we're providing the basin a comprehensive plan," with the "best balance" possible.

In the 200 years since William Clark and Meriwether Lewis first explored its length, America's longest river has been dammed, narrowed, deepened and straightened for commercial barge traffic so that it is some 100 miles shorter than the 2,500 miles navigated by their expedition, according to environmental group American Rivers.

Its water irrigates millions of acres of farmland, provides drinking water, cools homes, fills reservoirs and provides a waterway for barge transportation of farm products used by people throughout the United States and abroad. Its once ferocious spring floods are now history.

But the Corps, which manages the nation's rivers by building levees and dams and dredging to maintain navigation has been sued repeatedly from all sides by parties wanting either more water or less, or a more natural flow to the river. The whole problem has been worsened by a continuing drought in the West, where mountain snowmelt gives rise to the river.

Major suits were consolidated and a federal judge had ordered the Corps to come up with a plan by March 19.

The Corps said its plan is a compromise aimed at protecting endangered fish and birds, conserving enough water in upstream states to allow for recreation and other uses, and maintaining at least the minimum amount of water needed for barge traffic.

HABITAT FOR FISH, BIRDS

Under the plan, which the Corps estimates will cost $1.3 billion over 30 years, about 1,200 acres will be immediately established as a shallow-water habitat for spawning fish, while an unspecified amount would be designed to benefit nesting birds.

The plan aims to maintain a seven-month navigation season.

"Generally we should be able to provide the same level of flood control as the current plan," said Larry Cieslik, chief of water management for the Missouri River.

Upper-level management of the river calls for conserving more water in the northern states and "unbalancing" the three largest reservoirs, in Montana, North Dakota and South Dakota. The Corps would lower one of three lakes about three feet (one meter) to allow vegetation to grow around the rim and then refill the lake, on a rotating three-year cycle.

Environmental groups attacked the plan as doing too much for business interests. Missouri Gov. Bob Holden said the plan didn't go far enough to protect farmers and barge businesses.

"The Army Corps has a legal obligation to prevent endangered species from going extinct and a moral responsibility to manage the Missouri River for the benefit of the public at large," Chad Smith, a spokesman for American Rivers, said in a statement. "Today, the Corps dashed our last lingering hopes that they will show leadership without an explicit court order."

Holden said in a statement the plan was "not acceptable," and he was considering legal action against the plan, which he said ran counter to promises made by the Bush administration.

North Dakota also objected, saying not enough water would be retained for the state.