Buying new parklands: who will fill Uncle Sam's shoes?

The race is on. With the Reagan administration opposed to establishing any new parks, conservation groups are scurrying for money to buy open land before developers' bulldozers move in.

Conservationists won a partial victory last summer when Congress appropriated call for a moratorium on federal land purchases.

But that appropriation and a similar amount initially approved in Congress for 1982 continue a downward trend in the amount of money being spent on new parklands - an amount that peaked at more than $800 million in 1978.

The moves by Congress have not entirely settled the question either. In a recent letter to key congressmen dealing with environmental issues, Secretary Watt once again reiterated his conviction that all available funds should be spent on existing parks - not on acquiring new ones.

In the past, states have played a signficant role in preserving open land. But a recent budget-cutting move eliminated all federal funds normally appropriated for state land-buying programs.

Some states, such as Maine, have leftover federal money that may last several years. California generates $35 million a year for its parks by leasing tideland oil-drilling sites. But many other states have grown dependent on the federal matching funds to serve as an incentive for generating their own revenue, and many of these less fortunate states are considering issuing bonds to pay for new land.

The federal government's reduced role in land buying, combined with the elimination of state funds, has left preservation largely in the willing hands of private conservation groups.

''As our partnership with government diminishes, we are quite willing to take up the challenge the administration has laid down for the greater role of the private sector,'' says Greg Low, executive vice-president of the Nature Conservancy.

There are three major preservation organizations, plus scores of smaller land trusts, currently involved in land buying. The Nature Conservancy has 270 land preservation projects and 1.8 million acres under its protection. The National Audubon Society owns approximately 250,000 acres nationwide. The Trust for Public Land, which purchases land and then turns it over to states, the federal government, or other conservation groups, has been involved in 147 transactions totaling more than $60 million and covering 40,000 acres of land.

Conservation groups must rely on contributions from foundations, corporations , and individuals, and, though these contributions are up, they by no means fill the gap left by the federal government.

As a result, preservation groups are exploring alternatives to land acquisition. The Nature Conservancy, for instance, seeks agreements whereby landowners inform it if they plan any change in the use of environmentally sensitive land, or give the Conservancy 30-days notice if they intend to sell their property.

Other techniques include: setting up a stewardship fund in advance of any purchase to ensure there always will be money for maintenance of the land; selling grazing rights; arranging long-term leases so that the land will be protected but the landowners can continue to work it.

For its part, the federal government proposes that states take the similar kinds of action. William Hartwig, staff director for land policy at the US Department of the Interior, explains that the department is developing a policy to encourage states to augment their property by exchanging land, or by seeking rights of way or ''scenic easements.''

Conservation groups regard the race for money as particularly galling since the government had a built-in funding mechanism for buying parkland. Revenue from offshore oil leases, which now total billions of dollars, was legally earmarked for the Land and Water Conservation Fund, from which land buying money is appropriated. But now that is being diverted.

With visitation up 20 percent in Western parks in recent years, some conservationists answer the argument that funds are needed to maintain existing parks with a ''supply side'' theory of land acquisition: Acquire new parks, and vacationers now crowding into the old ones will fan out into the new. This, they say, would reduce wear and tear on overburdened facilities and eliminate the need to commit all the money for maintenance.