Decision on Gnatcatcher’s Status Delayed : Wildlife: Officials postpone action on listing the bird as endangered pending scientific opinion on whether it is the same as a subspecies common in Mexico.

U.S. wildlife officials on Thursday postponed a decision for up to six months on adding the California gnatcatcher to the endangered species list, saying that they want clarification of a narrow scientific point.

The U.S. Fish and Wildlife Service is waiting for an answer to a highly technical question of taxonomy: Are Southern California gnatcatchers a separate subspecies from similar gnatcatchers thriving in Mexico? The wildlife agency has urged a national panel of ornithologists to rule quickly on the issue.

Environmentalists charge that the White House pressured the Fish and Wildlife Service to delay a decision on the contentious issue until after the November elections. But the press secretary for U.S. Interior Secretary Manuel Lujan Jr. called the allegations “absolutely preposterous.”

“It has absolutely nothing to do with political issues. It has everything to do with science,” Interior Department spokesman Steve Goldstein said.

An influential group of Orange County and San Diego County developers opposed to the listing raised the subspecies question and requested the extension.

Robert Ruesink, a top supervisor in the Fish and Wildlife Service’s regional office in Portland, Ore., said officials within the federal agency believe the two birds are separate subspecies. But they decided after much internal debate that they want concurrence from the American Ornithologists’ Union.

Ruesink, chief of endangered species listings in the regional office, said: “What we’re trying to do is look at the possibility of legal challenges. We believe it is a valid (subspecies), but we want concurrence . . . which will shut down all of this ‘he said, you said.’ ”

When asked if the gnatcatcher will eventually be declared an endangered species, Ruesink said, “My answer is yes, I believe it will be listed.”

Southern California’s building industry contends that there is no proof the California birds are substantially different from the birds in Baja California. Because there are several million gnatcatchers in Baja, they say, the species should not be considered endangered.

Wildlife biologists and environmentalists argue that the only researchers who doubt that Southern California’s birds are distinct are working for the Building Industry Assn. and Chevron Land and Development Co.

Supporters of the listing say that the Fish and Wildlife Service seized the taxonomy issue to justify a decision that was politically motivated.

“I think it’s a concocted excuse,” said Jonathan Atwood, an ornithologist who has studied the gnatcatcher for 10 years and whose research forms the basis of the proposal to list the bird as being endangered.

Local builders said they were relieved to learn of the extension, and will use the time to collect more data to oppose the listing.

The Fish and Wildlife Service has been studying gnatcatcher data for three years. A year ago, the agency proposed giving the bird endangered status and had one year under law to make a final decision. A one-time extension of up to six months is allowed only if substantial scientific debate surfaces.

Conservationists say the plight of the gnatcatcher is a sign that Southern California’s ecosystem is in peril. From 66% to 90% of the birds’ habitat, a mix of brush called coastal sage scrub, is gone. But builders have lobbied against listing the bird as being endangered because it could stop or delay millions of dollars worth of development and roads.

“When you have this kind of economic impact you have to make darned sure your science is credible and right,” the Interior Department’s Goldstein said.