The Trust for Public Land likes to think of itself as a sort of Robin Hood--riding into the thicket of private landholders, armed with little more than the U.S. Tax Code, trying to save a little more of Sherwood Forest for posterity.

Since it opened shop in 1973, with $700,000 in seed money from private foundations, the trust has acted as the go-between in nearly $80 million worth of land sales to public agencies.

Despite budget cuts and the Interior Department's no-acquisition policy, more than $28 million of those transactions came in the first year of the Reagan administration.

Such "middleman" arrangements with nonprofit organizations are not uncommon. In some cases, they are initiated by the federal government as a way to safeguard threatened lands until purchase money can be authorized and appropriated.

In other cases, nonprofit groups are able to reach amicable agreements with private landowners who won't talk to the federal government. In still others, the nonprofits are able to use their tax-exempt status to arrange bargain sales and gifts that are financially attractive to both the landowner and the government.

The trust claims it has saved taxpayers more than $20 million by getting land at bargain prices and reselling it to government entities at less than the fair-market value.

But in the process, it has earned for itself more than $7 million, and that irritates the Interior Department.

In an effort to curb the practice, Interior has put out a new set of guidelines for transactions between nonprofit groups and federal agencies.

The guidelines, which take effect Sept. 25 unless they are modified, call for full disclosure of the financial arrangements between nonprofit groups and private landowners in any instance in which the federal government has been asked to deliver a "letter of intent" to buy the land.

The idea behind the guidelines, according to Interior official William Hartwig, is to keep nonprofit organizations from leveraging their land deals by, in effect, using the federal treasury as collateral.

"If they close the deal with their own money, that's no concern of ours," said Hartwig.

The Trust for Public Land appears to be taking the new guidelines in stride. It has no letter of intent for the purchase of Sweeney Ridge, for example, and Rosen said the trust won't ask the government for assurances on future deals.

"We have never collateralized with a letter of intent," he said. "We finance our own acquisitions."