As biological species go, the orange-footed pearly mussel might be in better shape if it were the only source of some rare and prized type of pearl.

Alas, as best anyone can tell, the mollusk -- also known as the pimple-backed mussel for the bumps on its shell -- has no such commercially redeeming value. It simply exists -- and barely -- along the murky bottoms of the Tennessee, Cumberland and Ohio rivers, surviving in such precariously small numbers that it has earned a place on the federal list of endangered species.

The world is definitely not this mussel's oyster, and things could get worse. A few weeks ago, the government agreed to consider whether some of the mussels should be sacrificed to make way for a 125-barge loading facility on the Ohio River in Illinois.

The Consolidated Grain and Barge Co. of St. Louis wants to build the facility, despite an opinion from the U.S. Fish and Wildlife Service that the construction would jeopardize the mussel's limited remaining habitat. Last April, the wildlife service suggested that Consolidated look into renting space from some of the 12 barge-loading facilities already in the area.

Consolidated instead appealed the case to the highest authority available under the Endangered Species Act -- a special panel of seven Cabinet members headed by the Interior secretary and known around the department as the God Committee.

Interior agreed this month to consider the barge company's request for an exemption from the law's strict rules against damaging an endangered species. The process starts with a prehearing before an administrative law judge next month and will end, if all goes according to plan, with a committee ruling by June.

The special panel owes its existence to the snail darter, the famous fish that held up construction of the Tellico Dam until Congress created the exemption process to let work on the dam proceed.

According to Interior officials, the committee has been called on rarely since then. Most conflicts between protected species and developers are resolved more or less satisfactorily at a lower level, often by altering development plans to avoid damaging a habitat.

Despite its less-than-esthetic name, wildlife specialists consider the pimple-backed mussel an appealing creature. "This one is very pretty," said Fish and Wildlife spokesman Megan Durham. The mollusk grows up to 95 mm in diameter (about 3.7 inches), with a heavy, nearly circular shell that ranges in color from yellowish-brown to chestnut.

The mussel used to thrive in a number of U.S. waterways, ranging down into West Virginia. Silt, pollution and dams have restricted it to parts of the upper Tennessee, Cumberland and Ohio rivers, and "it is extremely rare in all three," Durham said. "We haven't found any in any other streams."

ONCE BITTEN, TWICE SHY . . . Interior is maintaining an ironclad rule of secrecy on the subject of a court settlement to resolve a longstanding water dispute with a powerful California irrigation district.

Two months ago, the department was reportedly close to settling the four-year-old lawsuit on terms favorable to the Westlands Water District near Fresno. According to Rep. George Miller (D-Calif.), the district stood to receive millions of dollars worth of federally subsidized water for land that had been brought under irrigation illegally.

The department has been taking lumps ever since, not the least of them from other western irrigation districts that fear a backlash that could jeopardize their own water interests. Secretary Donald P. Hodel has made only one public comment on the matter -- and that was in a letter to several California newspapers denying that any deal had been concluded.

Miller succeeded in persuading Congress to block any settlement until at least April 15, and then only after congressional review. The arrangement does not give Congress the right to veto the settlement, but the public review is expected to dampen Interior's enthusiasm for what Miller called "a massive giveaway" of subsidized water.

"They could still put their heads down and march against the public interest," said an aide to Miller. "But once the confidentiality was blown open, the agreement started taking on water."