Wildlife Oasis Needs Protection. Urban development and pollution threaten New Jersey's Great Swamp Refuge. ENVIRONMENT: ENDANGERED REFUGE

ONLY 26 miles west of the hurly-burly of New York's Times Square, suburbia's shopping malls and parking lots give way to nearly 7,000 acres of swamp woodland, cattail marsh, and grassland. Nestled in a shallow basin ringed by flat-topped ridges, the Great Swamp National Wildlife Refuge is a haven for 300 species of wildlife, including mink, foxes, great blue herons, and American black ducks. Each year, it also attracts 300,000 visitors, who find the Great Swamp an oasis of open space in the nation's most densely settled state.

The Great Swamp was declared a National Wildlife Refuge in 1960, after a year-long battle that pitted a grass-roots coalition of Morris County citizens against the New York and New Jersey Port Authority's proposal to pave the wetlands into the metropolitan area's fourth jetport.

Now the Great Swamp Refuge faces a far more insidious foe - encroaching urbanization.

Recently the Wilderness Society listed the Great Swamp Refuge among the 10 ``most endangered'' refuges in the national system. In its report, the national conservation group declared that the wildlife refuge system was badly neglected by the Reagan administration, and ``is now at the low point of its 85-year history.''

The most serious problems facing many of the 445 national wildlife refuges include chemical runoff from farming, timber cutting and oil drilling on refuge land, and commercial development on refuge boundaries, according to the society. ``These actions are robbing the nation's beleaguered wildlife of habitat,'' the report said. ``More and more wildlife is becoming homeless every day.''

In placing the Great Swamp Refuge on its 10-most-endangered list, the society said waste water containing highly toxic PCBs has been found in effluent flowing directly into the refuge from two sewage treatment plants. Fertilizer and pesticides in water runoff from lawns also pollute the Great Swamp.

The wetland area is further scarred by a five-acre asbestos dump ``which is serious enough to be a Superfund candidate, and two landfills that may contain hazardous substances,'' the Wilderness Society reports.

``We can't keep abusing the Great Swamp and expect to see it survive as we've known it,'' says Bill Reffalt, the Wilderness Society's program director for national wildlife refuges. ``If action isn't taken to save it, [the Great Swamp] will be doomed within 20 years.''

ON a gray, late winter day at the Great Swamp Refuge, the sun struggles to highlight the naked branches of large old oak trees and the tips of last year's cattails. Bill Koch, manager of the refuge, sights a red-shouldered hawk heading for a patch of moist woodland. The wildlands belie the great maw of urban sprawl lying just beyond the refuge's boundaries.

Mr. Koch agrees with the Wilderness Society's contention that many of the refuge's most serious problems are tied to growing residential and commercial development within the Great Swamp watershed.

``Home rule,'' whereby each of the watershed's 11 municipalities makes land use decisions independently, fosters uncoordinated sprawl, according to Koch. Yet he resists the Wilderness Society's call for a regional planning commission that would coordinate development within the watershed.

``It's a good idea, but we don't think we could pull it off,'' he says. ``We've made overtures to township planning commissions to work with us, but some of them get real touchy. You can't go in and tell them how to run their town.''

Between 1963 and '79, 1,600 acres of wildlife habitat in the Great Swamp watershed were lost, yet urban growth continues largely unabated. Municipal zoning maps project almost complete development of privately owned watershed land by the year 2000, the United States Fish and Wildlife Service reports.

Local planners contend that even in private hands, much of the watershed remains open. According to Dudley Woodbridge, Morris County planning director, the Great Swamp watershed is zoned largely for low density residential housing - one house per two- to three-acre lot.

State conservationists consider the Great Swamp to be a jewel among New Jersey's public lands, both for its unique natural features wrought by the retreating Wisconsin Glacier 25,000 years ago and the fact that it was saved from the bulldozers when a group of volunteers raised more than $1 million to purchase nearly 3,000 acres of the wetlands.

Subsequent land acquisitions have brought the Great Swamp Refuge to its present 6,936-acre total. In 1968, half the refuge became the East's first officially designated wilderness area, to be forever preserved in its natural state.

In addition to offering visitors a respite from the pressures of urban life, the Great Swamp controls flooding by sponging excess water during heavy rainstorms so that it does not overrun areas downstream.

Yet stepped-up development and the blacktopping of much of the surrounding watershed is causing greater and faster water runoff, leading to flooding in the refuge and the destruction of waterfowl nesting sites, according to the society.

Local planners dispute this, arguing that three major dike systems, built by the Fish and Wildlife Service to hold water in times of drought, instead encourage flooding during rainy periods.

The wetlands also act as a natural filter for rainwater that passes through it and is later consumed by downstream communities. Yet according to the Fish and Wildlife Service, the Great Swamp basin's natural filtration system ``may ... be near or exceeding its capacity.''

The Wilderness Society is calling for the purchase of private parcels on the fringes of the refuge to combat flooding and degraded water quality caused by overdevelopment. But the Fish and Wildlife Service reports that it lacks the funds to acquire even those lands already approved for acquisition. Meanwhile, the service notes, development continues ``at an alarming rate.''

``The Great Swamp has withstood all the insults it can sustain,'' says Helen Fenske, assistant commissioner of the state Department of Environmental Protection. ``Without help, it is fast becoming little more than a sump pump for waste water.''