A giant lawsuit over the Western Area Power Administration's management of Western dams would have been settled Thursday - except that environmentalists filed a new suit two days before, according to lawyers.

The original action by Utah Power & Light Co., Salt Lake City and 143 other cities over the federal government's power generating and marketing practices has been pending since October 1986. Claims involving power sales were dismissed, leaving only environmental matters to be resolved.Settlement negotiations dragged along for months, until the parties were on the verge of inking an agreement.

Then on Monday, the National Wildlife Federation, Grand Canyon Trust, America Rivers Inc. and Western River Guide Association filed their own suit against the government's dam operations. The new action claims that new power marketing criteria for Glen Canyon Dam and Flaming Gorge Dam could harm downstream habitat.

U.S. District Judge J. Thomas Greene had scheduled what was billed as a settlement hearing on the original suit for Thursday. He opened it by saying he only knows what he reads in the newspapers - meaning he read about the environmental suit.

Max C. Vassenelli, a lawyer for the government, told Greene that the suit was "settled to all practical purposes." Until Monday, it awaited only the signatures of the parties.

The new suit - a mirror image of the earlier one - has caused a delay, he said.

Donald B. Holbrook, representing UP&L and the 143 cities, asked that the settlement conference be delayed for 30 days, while the parties try to iron out the new wrinkle. "The likelihood of settlement is still very much before us," he said.

Greene set a new settlement hearing for 9 a.m. on Jan. 30.

Wayne Petty, lawyer for the environmentalists, had filed a motion with Chief Judge Bruce S. Jenkins, to whom the environmental suit was assigned, asking him to consolidate it with the earlier action.

Immediately after the session before Greene, the lawyers marched in a pack to Jenkins' chambers, telling him the parties in the earlier suit are opposed to consolidation.

Petty told the Deseret News he believes parties in the first suit will try to have his dismissed.