In an unusual series of squabbles, top Justice Department officials have ignored the wishes of their client, the Interior Department, and have backed Indian tribes' positions in three important cases over western water rights.

Although they turn on technical legal points, the cases involve key political and economic issues surrounding the use of scarce water in the arid West. The disputes pit powerful western landowners, who have prospered through federally sponsored irrigation projects, against Indian tribes who have become increasingly active in asserting their rights under longtime treaties with the federal government.

It is rare for the Justice Department to reject the wishes of an agency that, in this case, had to choose between the interests of competing constituents, traditionally represented by the Bureau of Indian Affairs and the Bureau of Reclamation.

In a case to be argued April 27 before the Supreme Court, Solicitor General Rex E. Lee and Assistant Attorney General Carol E. Dinkins rejected Interior Solicitor William H. Coldiron's recommendation to back the state of Nevada and an irrigation district against a claim by the Paiute Indian tribe for water to restore the fishing at Pyramid Lake near Reno.

More than 60 years ago, Interior officials decided to divert water to a nearby reclamation project to benefit white farmers instead of asserting the tribe's claim. Over the years, the lake dried up, its trout died--and the tribe eventually went to court.

But Coldiron argued in a letter to Dinkins last summer that a subsequent court decision that redistributed the water shouldn't be reopened even though the government's treatment of the tribe in the 1920s "may have been improper."

Two weeks ago the Supreme Court ruled, 5 to 3, that a similar 1963 case settling water rights on the Colorado River couldn't be reopened, even though the government had not claimed all the land that it should have when the case was first argued in the 1950s.

The dissenting justices questioned the "quality" of the Justice Department's representation of the Indians when the case first arose. But several legal experts said that Justice attorneys David R. Warner and Walter Kiechel Jr. had won a huge victory for the five tribes using the Colorado River when the case was first decided.

Justice lawyers argued in that case that the department couldn't find the cause of the mistake. But in the Pyramid Lake case, Lee and Dinkins flatly admitted that the government had "plainly breached its trust obligation to the tribe" years ago.

In another current Supreme Court case--centering on whether such cases should be heard in state or federal courts--Lee and Dinkins wouldn't go along with Coldiron's recommendation to side with the states as part of the administration's "new federalism" effort.

In a letter to Dinkins last summer, Coldiron said, "The resolution of these issues has a direct bearing on the relationship of the United States to Indians and Indian tribes in water right matters and the manner in which the United States . . . assists the western states in attempting to meet the anticipated water crisis of the next decade."

In a third case, which hasn't reached the Supreme Court, Justice attorneys decided to appeal a 1980 decision settling rights on the Carson River in Nevada, although Interior officials and Sen. Paul Laxalt (R-Nev.) opposed the idea. Laxalt wrote Attorney General William French Smith in August, 1981, asking that the appeal be dropped.

"Apparently, the only parties not completely satisfied with the decree are a small number of Indians and some attorneys within the Department of Justice," he said.

He added that Interior officials agreed with him, and said Justice lawyers seemed to be appealing for the sake of "proving some obtuse legal point."

If the Indians win, they could get more of the water that western states already are fighting for among themselves. The Pyramid Lake case illustrates the high stakes.

Nevada and the 16 other states that support its position in friend-of-the-court briefs argue that the finality of earlier court decisions--and the billions of dollars of investment that followed them--must be protected.

The tribe, the Justice Department and some environmental groups counter that the government's failure to assert the Indians' claim 60 years ago must be corrected.

"Any trustee . . . lacks the authority to deal away a beneficiary's 100-square-mile lake to more favored parties behind closed doors," Charles Wilkinson of the University of Oregon Law School wrote for a group of professors representing the Sierra Club and Friends of the Earth. The farmers should be able to conserve water that is now wasted, he argued.

The Pyramid Lake case also illustrates the conflicts raised when the government tries to represent competing interests--such as the irrigation of western lands under the Reclamation Act of 1902 and the reserved water rights of Indians, a doctrine first enunciated by the Supreme Court in a 1908 case.

In 1922 an Indian agent named Lorenzo Creel wrote his boss in Washington suggesting that the government assert a claim for more water for the Indians' Pyramid Lake. In a similar letter to a supervisor in Reno, Creel wrote:

"Neither the reservation officials nor the Indian Department had any vision of almost the whole volume of the Truckee River being diverted away from its natural channel and carried in a vast canal away over into the valley of another stream and there spread out over thousands of acres of desert lands cultivated by white farmers."

The acting head of Indian affairs at Interior responded that he would do what he could to protect the fish "so far as consistent with the larger interests involved in the proposition having to do with the reclamation of thousands of acres of arid and now useless land for the benefit of the country as a whole."

In his letter to Dinkins last July 16, Coldiron wrote that the government "may have acted improperly" in not asserting the tribe's claim a half century ago. But he said the tribe should have raised the issue itself before the final decree was entered.

The 9th U.S. Circuit Court of Appeals ruled that Interior didn't have the authority to subordinate the Indians' water claim to the reclamation project, and directed a lower court to determine how to distribute the river's water between the Paiutes and the farmers.

Coldiron wrote that this put the United States "in the untenable position whereby it must argue to jeopardize the viability of the very project that it is statutorily charged to protect by the Reclamation Act of 1902 . . . . In effect, the 9th Circuit is requiring the government to 'cut off its nose to spite its face,' which is apparently unacceptable where Indians are concerned, but not where other federal interests are at stake."

The Justice brief, however, said the U.S. breach of trust was "of such a nature and magnitude" that the tribe's water right should be relitigated, despite the 1944 settlement.

Coldiron couldn't be reached for comment. Dinkins and Lee declined to discuss their differences with Interior. But Lee said, "In some instances it is simply that there are other considerations that may bear on the interests of the government that the agency may not be aware of. That lies at the root of why we have a Justice Department and solicitor general. You have to have someone funnel all litigation to the Supreme Court, someone who can see the big picture."

Dinkins said, "This position indicates that we take this trust responsibility seriously and will do what is necessary and appropriate to discharge it."