The Orange County Board of Supervisors yesterday transfered 1,200 acres of prime open space to the Rancho Mission Viego Land Trust. The land is part of the Donna O'Neill Land Conservancy, which was created to offset development in 1990. Although the Land Trust states that it will intregrate this land into its open space preserve and keep it undeveloped, opponents of the proposed extension of the Orange County Foothill-South toll road fear that the land my eventually turned over to the toll road developers. Current plans for the toll road call for it to go through the Donna O'Neill land. Both the Board of Supervisors and Rancho Mission Viejo support the toll road.