A coalition including almost all the nation's major environmental groups yesterday denounced the Carter administration for breaking its word and "subverting" promised federal water policy changes.

Carter last year promised major water policy "reforms" to halt the building of expensive, sometimes environmentally destructive dams, provide incentives to cut down water consumption, and stop subsidizing large irrigation, navigation and other commercial interests.

But the administration, according to the Coalition for Water Project Review, is now "dancing to a different sacrificing rivers, streams and wetlands to the demands of narrow groups and powerful beneficiaries."

The harsh denunciation - voiced at a press conference by representatives of the coalition, and of the Natinal Wildlife Federation, the National Wildlife Federation, the National Audubon Society and the Environmental Policy Center, all coalition members - represents a major break between the Carter administration and the environmental community which has so strongly supported it.

It was a frank attempt to change the direction of the upcoming water heavily influenced by western politicians and congressional dam-builders. The policy statement, now under review in the White House, is expected to reach Carter's desk in a few weeks, but administration officials have already conceded that several major reforms" are politically unfeasible.

The coalition specifically attacked Vice President Modale and Interior Secretary Cecil D. Andrus, Andrus has "made one concession after another," coordinator John Burdick said, citing recent approvals of Denver's Foothills project and North Dakota's Garrison irrigation project, both of which environmentalists strongly oppose.

Mondale has refused to meet with conservationists, but in a trip out West spoke almost exclusively to "the powerful resource extractors - timber interests, mining interests, cattlemen and water development interests," Burdick said, adding that Mondale "has been active behind the scenes to water down [promised] reforms."

In a separate letter to Mondale, the Natural Resources Defense. Council said his staffers were undermining "reforms" by advocating only minimal repayment of dam construction costs by proposing to exempt states from environmental revisions if they pay part of dam costs and by opposing a strong policy to maintain sufficient water in streams for cities, fish and wildlife.

Thomas Kimball of the National Wildlife Federation, the nation's largest conservation group with 3.5 million members, said a recent membership poll revealed "they clearly feel the Carter administration is retreating from the promises it made in the past."

The federation is especially disturbed that administration officials apparently won't try to increase the so-called discount rate applied to a backlog of 828 projects. Congress authorized these projects over the years using a rate as low as 3.25 percent to calculate long-term benefits - a formula which makes marginal projects look economically attractive.

"This kind of manipulation of costs and benefits cries out for reform," Kimball said. Not changing the discount rate - a decision which ultimately rests with Congress - would "make a mockery of Carter's water policy," he said.

Kimball and other coalition spokesmen also criticized the administration for backing off mandatory water conservation. "Before new water supply projects are funded, plans for enforcing water conservation should be in place, including sensible pricing in water-short areas," Kimball said.

Approving Denver's Foothills Water treatment plant and dam, said Brent Blackwelder of the Environmental Policy Carter, is "dramatically at odds with the president's goal of water conservation. Were water meters installed, water pricing reformed and water-saving devices put in place, there would be no need for Foothills."

The environmentalists also criticized the administration for moving toward approval of Colorado's Narrows Dam, which Carter had opposed last year. The dam would seriously harm wildlife, present a safety hazard and create water pollution, said National Audubon Society President Elvis J. Stahr. Yet Andrus has allowed a "whitewash" report of the project by the Bureau of Reclamation "to placate western interests," he added.

Stahr also attributed Interior's plan to allow construction of a major dam and reservoir in North Dakota's Garrison project to "political motives." It will result, he said, in "an incredible and outrageous subsidy of $1.1 million per farm."

Both Andrus and Mondale were out of town yesterday, but issued statements through their offices. "Our critics seem to be crying before they are hurt," Andrus said. "My water policy recommendations have not even gone to the President yet.

"As for the individual water projects, we stand accused of listening carefully to both sides and trying to be fair and responsible. I hope we can get past the grandstanding phase of this whole debate and down to the merits."

Mondale has been represented in water policy discussions by his assistant Gail Harrison and Bertram Carp of the domestic policy staff.

His office said: "While the vice president has not yet reviewed agency recommendations, he has instructed his staff to follow the matter closely. This study is being undertaken in the context of the president's commitment not to preempt state or local water rights."

The Coalition for Water Policy Review is made up of 24 major conservation groups, among them the Sierra Club, Friends of the Earth, Environmental Action, the Izaak Walton League, the Environmental Defense Fund and the four groups cited above.