Congressional Country Club on River Road in Bethesda is known as the annual host of the Kemper Open, a golf tournament that raised $110,000 for charity this year.

Unexpectedly, there is another side to this golf club--its "refuge." The manager of the greens and grounds, C. William Black, has attracted bluebirds--which have declined dramatically in population in this century--by building 60 houses for them on trees that line the 500-acre course. The birds, in turn, are eating harmful insects.

Black researched the subject in books obtained from the North American Bluebird Society office in Silver Spring.

Bluebirds, along with purple martins, which nest in high-rises Black has installed for them, are considered nice birds to have around because they eat great quantities of caterpillars, grasshoppers, cutworms and other harmful insects. This is especially true when they are raising their families, which range in size from three to six fledglings per nest. At this time, parents forage for food from dawn to dusk to feed their voracious young.

"They are cavity-nesting birds, which means that they use old tree stumps or old wooden fence posts that have a hole or cavity," Black said. But the woods around Washington have been carved up for construction, causing the habitats of the birds to change.

"Dead tree stumps are removed and there aren't any old wooden posts now; they've been replaced with metal posts," Black said. "So they really have no place to nest. They are looking for places."

Danny Bystrak of the Patuxent Wildlife Research Center said the severe winters of both 1977 and 1978 depleted the bluebird population. Only in the last few years, he said, have the birds started to make a comeback.

English sparrows and European starlings drive bluebirds out of their nests, a spokeswoman for the bluebird society said. Those aggressors sometimes even peck bluebirds to death, she said.

Nesting boxes with small openings are recommended to help protect bluebirds. The bluebird society says an opening of 1 1/2 inches prevents starlings from entering but won't stop the smaller sparrows.

Sparrows can be evicted from bluebird boxes, although it sometimes takes many tries before the birds are discouraged, the bluebird society said.

To deter the sparrows, Black periodically makes the rounds of the houses. He can tell a bluebird is in residence if the nest is all of one material, such as moss or pine needles. Other birds, such as sparrows, use a mixture of rags, paper or anything else they can get, Black said.

In a tour of his course, Black listed some of the other residents of the grounds: They include deer (a doe and her twin fawns), woodchucks, foxes, muskrats, crows, frogs, tadpoles, a goose and two goslings, trout and bass (which live in the seven ponds) and painted turtles. A beaver dropped by this winter, but "he didn't stay long," Black said.

As Black was checking one of the bluebird boxes, a flying squirrel emerged. It posed for a second, then scurried up a cedar. Black said he usually is very cautious about opening the boxes because sometimes bees nest in them; once he encountered a black snake.

Although bluebirds seem to be coming back, it is only to certain areas, the bluebird society said. But where people are installing "bluebird trails"--a series of nesting boxes posted on trees, they are doing well, a spokeswoman said.

There are trails in Beltsville, at the NASA Goddard Space Flight Center and on Rossmoor's golf course. Bluebird society official Mary Janetatos says other golf clubs are being enlisted.