The scrubby, rock-filled drainage ditch at the end of a runway at Los Angeles International Airport might not look like much, but to scores of endangered shrimp, it is home.

The little depression, surrounded by a chain-link fence with signs warning "Los Angeles World Airports -- Endangered Species -- Keep Out," is part of a 108-acre area at the airport that federal officials want to designate as a preserve for the tiny creatures.

The proposal by the U.S. Fish and Wildlife Service, announced earlier this year, took Los Angeles World Airports, the city agency that operates Los Angeles International, and the Federal Aviation Administration by surprise. The agencies have spent years trying to persuade federal wildlife officials to allow them to move the airport's Riverside fairy shrimp population.

At many airports in California, including Los Angeles International, rare birds and animals have found refuge from relentless coastal development. But the desire to provide a haven for endangered species at these airports often conflicts with aircraft safety.

Airport officials argue that creating a preserve for the shrimp poses a risk because the crustaceans require standing water, which attracts birds and other wildlife. Birds, in turn, can be sucked into aircraft engines.

The airport logged 632 "wildlife strikes" -- in which a bird or other animal collided with an airplane -- from 1990 through 2004, FAA officials said. Those encounters caused severe damage to some planes and endangered people on board and on the ground.

In the most serious incident at Los Angeles International, a seagull was sucked into one of the four engines of a KLM jumbo jet during takeoff in August 2000 with 449 people aboard. The collision threw the engine's spinning turbine blades out of balance, sent chunks of metal flying and knocked off the tail cone.

The heavy tail cone landed on a beach a few feet away from a family. The plane made an emergency landing. No people were hurt.

Fish and Wildlife Service officials said they had no choice but to propose designating 5,800 acres in five Southern California counties as a preserve for the Riverside fairy shrimp. A federal judge ordered the action in response to a lawsuit that invalidated a previous critical-habitat designation for the species that was finalized in 2001, said Jane Hendron, a service spokeswoman.

The airport is one of the last refuges for the declining population of the fragile crustacean, according to the Fish and Wildlife Service. Development, off-road vehicle use and livestock overgrazing have destroyed 90 percent of the shrimp's habitat in Southern California.

The service agreed this spring to allow the city's airport agency and the FAA to move a small number of shrimp to comply with mitigation measures required by the airport's modernization plan. Federal wildlife officials also have agreed to allow airport administrators to use a portion of the proposed preserve for other activities as long as they protect 23 acres where the shrimp lie.

But aviation officials are still trying to persuade the service to allow them to transplant the entire population.

Fish and Wildlife officials say they will continue to negotiate with the city's airport agency and the FAA over the shrimp's future.

Riverside fairy shrimp exist only in several Southern California areas. The translucent creatures, which reach half an inch to an inch in length in adulthood, inhabit warm freshwater pools that form during the rainy season. After they reach maturity, the adult females lay eggs, which sink to the bottom of the pool. The eggs remain in the soil after the pool dries up and lie dormant until it fills with water again.

The shrimp at the airport are stuck in the cyst, or egg, state and have not hatched for years. That is because the pools are too shallow and the water chemistry is off, aviation officials say, adding that too few eggs exist at the airport to allow the species to flourish.

No one knew Riverside fairy shrimp existed at the airport until biologists in 1998 started compiling a list of species to be included in environmental studies for airport modernization plans.

Those studies, conducted during one of the wettest years in more than a century, found shrimp eggs in nine locations, including in tire ruts, along the shoulders of access roads, in a hazardous-materials containment pond and in a flood basin.

But only a small percentage of the eggs were viable in a lab -- where it took two tries to hatch the crustaceans, said Andrew B. Huang, an environmental supervisor at the city's airport agency.

The airport in Los Angeles is not the only one struggling with accommodating endangered species. At San Diego International Airport, officials have worked for a dozen years to protect the endangered California least tern, which nests each year between the taxiways at the seaside facility. But because of its behavior and small size, the bird does not present a significant risk to aircraft.

Federal wildlife officials are not required to issue a final ruling on the Riverside fairy shrimp habitat proposal until the spring. In the meantime, airport officials are pulling together documents and completing studies they hope will persuade the service to allow them to move the shrimp.

Plans are underway to designate acreage at Los Angeles International Airport as a preserve for Riverside fairy shrimp, a fragile crustacean population.