In an unusual move, the Fairfax Board of Zoning Appeals delayed its scheduled decision this week on the American Horticultural Society's proposed expansion at the historic 27-acre River Farm and Wellington Mansion off Mount Vernon Parkway. The farm and mansion were once part of George Washington's Mount Vernon property.

The postponement was in response to a request from Mount Vernon Supervisor Warren Cikins and was the second time the board has delayed making a decision on the controversial proposal.

Cikins asked for a 90-day, but board members voted to consider the plan at their regular meeting April 18. They said no more public testimony on the issue will be accepted.

The board opened its meeting last month for further public testimony and accepted a petition signed by residents in the area opposing the proposed expansion. The petition was submitted by developer Gerald Halpin, the immediate neighbor to the south of River Farm. Included with the petition were comments on possible traffic impact and alternative proposals to the horticulture society plan.

Letters supporting the proposal also were submitted to the board, including one from Charles Cecil Wall, a resident and former member of the planning commission from Mount Vernon.

The community remains divided on the issue. The East of the Parkway Assosciation was unable to take a position because of divided opinion in its membership. The Wellington Civic Association opposed the expansion; the Waynewood Civic Association supported the proposal, and the Mount Vernon Council of Civic Associations voiced support as long as several conditions are met.

The horticulture society has asked the board for a special-use permit to build four Georgian-style office buildings attached by a walkway to the former carriage house and servants' quarters on the site. The society also plans to improve several other buildings on the property, expand the parking area and extend and improve the entrance and circular driveway. The society has agreed to give scenic easements to the National Park Service along East Boulevard Drive and an easement to the State of Virginia along the Potomac River.

The society's offices are in the main house, the Wellington Mansion, which would remain unchanged.

In the buildings, the AHS proposes to established a plant science data and library as well as to rent space to related non-profin-profit organizations such as the Herb Society and the Garden Clubs of America, Inc. Thomas Richards, executive director of AHS, said there would be no more than 100 employes from all organizations in the buildings.