Endangered peregrine falcons, such as those now raising a new brood of young on the 33rd-floor ledge of the USF&G; building in Baltimore, have made such a strong comeback they now may pose a threat to some other endangered birds.

"In the mid-Atlantic region, there are probably more peregrines than there ever were," said John Barber, a USF&G; employee and former Smithsonian Institution ornithologist.

Peregrines nesting on special towers erected on Assateague and Chincoteague islands on the Eastern Shore have become a particular problem.

The falcons are preying on endangered least plovers and piping plovers on Maryland's Assateague Island, Barber said.

"The solution, I think, is to . . . relocate the peregrines by taking down the towers they're nesting on, and that's very controversial," he said.

Another problem, he said, is that peregrines are aggressive and highly territorial. When Greenland peregrines migrate down the coast, "they're getting beaten up by the East Coast peregrines we have."

Baltimore's peregrines, at least, are innocent of such predation.

The city's gradual cleanup and restoration of wetlands along Middle Branch Park is attracting more shore birds to the downtown area, and providing the falcons with ready access to a diet cleaner and more varied than the pigeons that once sustained them.