The Interior Department yesterday extended emergency protection under the Endangered Species Act to two obscure fish species in an unusual Nevada desert valley, putting a $250 million resort development on ice for at least eight more months and perhaps forever.

The U.S. Fish and Wildlife Service took the action to save the Ash Meadows speckled dace and the Ash Meadows Amargosa pupfish from being snuffed out by Calvada Lakes, a resort community planned by Preferred Equities Corp. (PEC) of Las Vegas. An earlier emergency designation, approved by the department last May at the urging of Fish and Wildlife officials, expired yesterday.

The department also formally proposed to make the protected status permanent, signaling an end to two years of fruitless attempts to negotiate a land exchange between PEC and Interior's Bureau of Land Management, the principal landowner in the Ash Meadows area, a rare desert wetland in southern Nevada.

According to the Fish and Wildlife Service's Federal Register notice yesterday, "PEC found BLM lands . . . unacceptable because of inadequate water supply."

But Jack M. Soules, president of PEC, said yesterday that BLM had never made an offer of land in exchange for the fragile desert valley his company owns. He said had never talked to BLM officials in Washington, and regional officials have been hampered by a lack of guidance from headquarters.

"They've never offered any land that we've been able to accept or turn down," Soules said. "They're pretty hard people to talk to."

A BLM spokesman in Washington said negotiations were continuing, including a meeting held yesterday in Nevada between Soules, BLM's regional office and aides to Sen. Paul Laxalt (R-Nev.). But in a letter to its regional office in Reno Nov. 10, BLM said it had found problems with the land exchange.

The Calvada Lakes development is planned for a 13,000-acre parcel of land in Ash Meadows that PEC bought from agricultural interests in 1977, a year after the Supreme Court limited ground-water pumping to ensure the survival of the Devil's Hole pupfish, another rare native species. At least six other plant and animal species from the area are on the endangered list or are candidates for it.

Unfortunately for those living things, the valley's attributes make it ideal for human habitation as well. "It has nice lakes, 10 large artesian springs. It's a beautiful valley because of the water, which you don't find in desert valleys," said Soules.

PEC has already put more than $6 million into Calvada Lakes, and Soules said the firm intends to press on.

"In this day and age, I'm not sure how far federal powers extend over private owners and private lands," he said.

Sanctions under the Endangered Species Act are generally limited to projects with federal involvement, such as funding or loan guarantees. However, the act also has language relating to the "taking" of an endangered species, meaning that PEC could run afoul of the same provision that stymies trophy hunters.

Meanwhile, in what Fish and Wildlife officials called a coincidental announcement, Interior has issued a status report on 363 vertebrate species it has been reviewing for possible listing as protected species. The department said 62 of those probably will make the grade, and more information is needed on the rest. In addition, 38 species have been dropped from further review, 14 of those because they are believed to be extinct.

Interior Secretary James G. Watt has been criticized for failing to add species to the protected list, but a Fish and Wildlife spokesman said the new list does not represent a change in policy.

"It's just a lot easier if you list them all in one place," she said. "This is just a better way to do business."