Virginia Attorney General Mark R. Herring said Wednesday that he is satisfied that the donor whose $1 million gift allowed the American Horticultural Society (AHS) to purchase River Farm nearly 50 years ago would want the historic Potomac River property to remain forever undeveloped and open to the public.

And Herring said he was prepared to take legal action to ensure that the late Enid Annenberg Haupt’s wishes are upheld.

“We’ve not taken any options off the table,” Herring (D) told reporters at a news conference. “But, of course, our preference is that AHS continue to make sure and take steps that this property continue to be used for the purposes for which Ms. Haupt made the gift.”

Herring’s office has been trying to determine whether the AHS’s proposed sale of the historic property meets the terms of the grant that allowed for the group to purchase the land. The D.C. attorney general also has opened an investigation along the same lines because the AHS is chartered in the District. Herring said the AHS has been cooperative in the investigation.

The AHS did not immediately respond to a request for comment. On Tuesday, however, AHS board Chair Terry Hayes emailed members asking for their support of the proposed sale, saying it was financially necessary and would allow the nonprofit to build an endowment to support its horticultural programs on a national scale.

Hayes’s email also placed some blame on Fairfax County for the organization’s financial difficulties. She said county regulations that control its operating hours, parking, and the number of special events and visitors took a toll on its finances. She also said the county’s recent decision to create a “historic overlay district” that imposes additional restrictions designed to protect the property’s historical resources will only increase the organization’s operating costs.

She further suggested that Haupt would back the sale if she were alive. It was an assertion that critics of Hayes and the AHS’s current leadership said couldn’t be more wrong.

“It read like it was from ‘The Twilight Zone,’ ” state Sen. Scott A. Surovell (D-Fairfax) said.

About 30 people, many of whom are members of Save River Farm, attended Wednesday’s news conference outside the closed gates of the property. U.S. Rep. Don Beyer (D-Va.) sent a message of support.

“We’re all here for one simple thing: to protect and preserve River Farm,” Fairfax County supervisor Dan Storck (D-Mount Vernon) said.

The AHS put River Farm on the market for $32.9 million last year, saying pandemic-related closures had hurt its revenue from hosting weddings and special events. Hayes’s message on Tuesday went further, saying the organization’s attempt to maintain the 18th-century manor and grounds while also offering educational programs has been a struggle for decades.

Her email said that capital expenses, including a $1.2 million loan for sewerage and irrigation systems, grew more than spending on gardening programs. She said the cost for deferred maintenance is now an estimated $3 million.

And she offered an alternative explanation of Haupt’s gift to the AHS, saying she did so primarily because she wanted to keep the property out of the hands of the Soviet Union, whose embassy in Washington had explored buying the property as a retreat for its diplomats.

“I think if she were alive today and asked to make a choice between AHS becoming the conservator of River Farm or investing the sale proceeds in the future of AHS and horticulture in America, she would choose the latter,” Hayes wrote.

Surovell said ample documentation exists — including Haupt’s public statements, newspaper accounts of the AHS’s purchase of River Farm, her obituaries in the New York Times and The Washington Post, and the actual grant terms — to suggest Haupt wanted to preserve River Farm as a green space for the American public.

The Annenberg Foundation, which executed the grant allowing the AHS to obtain River Farm, wrote to the AHS last month, urging it to keep the property free of development and open to the public and reminding the organization that Haupt’s wishes were memorialized in the sales contract drawn up on December 1972 and in grant specifications laid out in January 1973.

Late last month, dissenting members of the AHS board also spoke out about their opposition to the proposed sale.

“Her intentions were clear,” Surovell said. He also criticized the AHS for its recent efforts to downplay River Farm’s historical significance. “This is about as historic a property as it gets in Northern Virginia,” he said.

Meanwhile, a coalition of preservationists, led by NOVA Parks and the Northern Virginia Conservation Trust (NVCT), has continued to negotiate with the AHS to buy the property. Alan Rowsome, NVCT’s executive director, said their most recent offer was about $16 million for the property, which is about $1 million below its current assessed value.

“It’s my sincere hope that the AHS board will listen to its neighbors,” Del. Paul E. Krizek (D-Fairfax) said. “We are here because we do not want to see paradise paved over.”