Bald eagle population isn't soaring, but it seems to be growing

America's endangered bald eagles are holding their own. The latest evidence of the comeback of the bird that is the United States national symbol comes in the National Wildlife Federation's annual bald eagle survey.

The report, released recently, found that in 43 of America's lower 48 states, the number of bald eagles sighted increased from 10,903 last year to 11,819 in 1984. The survey was conducted over a two-week period in January.

Although the survey is primarily intended to help wildlife biologists and state conservationists identify areas where eagles spend the winter months, the data are also used as a indication of the well-being of the eagle population.

''It at least tells us that the population isn't changing dramatically - that they are at least stable, if not increasing,'' says Brian Millsap, a raptor biologist with the National Wildlife Federation.

Mr. Millsap identifies prime wintering areas for eagles as the Mississippi River Valley, the reservoirs and rivers of the Great Plains, the portions of eastern Utah, and the Chesapeake Bay area.

In the late 1960s and early 1970s, bald eagle populations plunged as a result of the widespread use of the chemical pesticide DDT. The pesticide, when ingested, hindered the birds' ability to reproduce. The destruction of much of the eagle's natural habitat also contributed to the population decline.

DDT was banned in 1972, and efforts were begun to help revive the foundering eagle population. The results began to show in the late 1970s and early '80s.

Today, bald eagles are still listed as endangered in 43 states and as threatened in five. (Eagles are plentiful in Alaska, and there are none in Hawaii.)

Last year the US Fish and Wildlife Service conducted its five-year survey of the bald eagle population to determine if the birds should remain on the endangered list in various states. Federal biologists decided to maintain the endangered designation.

''We are pleased with what's happening, but we don't feel that what's happened to date warrants removal from the endangered list - not yet,'' says Paul Nickerson, an endangered species biologist and eagle expert with the Fish and Wildlife Service.

Mr. Nickerson says that more important than the January survey of wintering eagles is the summer count of nesting eagles in the US. He notes that many of the birds counted in the American winter survey are Canadian birds that fly south for the winter but that actually nest north of the US border.

The federal biologist estimates there are some 1,500 to 1,600 nesting pairs of bald eagles in the lower 48 states of the United States. He identifies prime eagle nesting areas in the US as the Pacific Northwest, the Great Lakes states, Florida, Maine, and the Chesapeake Bay area.

Nickerson, who is based in Massachusetts, says this has been the best year ever for biologists working to restore the eagle population in the Northeastern states. He notes that of 28 young eagles brought into the region from Canada in a restoration project, 27 have survived and are flying.

The Canadian-US restoration program is intended to boost the US population of eagles by bringing young eagles to artificial nests in the US. It is hoped that in five years, when the eagles mature, they will return to mate in the area where they first learned to fly.