A road grader dispatched by the Los Angeles Harbor Department partially destroyed a prime breeding area of one of California'a rarest birds Friday as several government agencies stood by unable to stop it.

It began Friday morning as the grader scraped off a layer of sand and occasional brush that had accumulated on a bleak corner of Terminal Island, an abandoned airstrip known as Reeves Field. The area has been used as a nesting ground by the California least tern four of the last five years.

Members of the least tern recovery team, a governmental committee formed to help ensure the survival of the bird, said the scraping, if completed, would render the area unsuitable for nesting by the terns.

"The only thing left out there (where the grader had scraped) is bare asphalt, and it's very unlikely the birds will nest where the sand and brush have been cleared,' said Paul Kelly, a Fish and Game biologist and member of the recovery team.

Alan Craig, a Fish and Game biologist and also a member of the recovery team, says the terns need the snd to lay their eggs and some occasional brush to use as shade for the young birds. "It gets very hot out there," Craig said.

The least tern, a small white bird with a black-capped head, is listed as endangered by both the state and federal government. Wildlife experts estimate that about 775 pairs remain. Last year, the experts say, the Reeves Field nesting site accounted for 80 young birds and was the second most productive breeding area in the state.

Harbor Department officials described the scraping as "routine maintenance." Lee Zitco, a spokesman for the department, said however, the last time such routine maintenance had been performed was three to four years ago.

Hurried phone calls to department officials by the federal Fish and Wildlife Service and the state Coastal Commission proved fruitless. Fred Crawford, general manager of the department, refused to stop the scraping, saying, "My job is to preserve the port."

In recent weeks the Harbor Department has prepared another site on Terminal Island for the least terns in hopes they will select that area rather than the Reeves Field site.

However , recovery team members, all wildlife specialists from several government agencies, say their own efforts to lure the tern to new sites in recent years have failed, and their concern now is that the tern will be left will no nesting area in the harbor vicitinity.