The Berlin porcelain sets, said to have been made between 1770 and 1775, are inscribed with the busts of Catherine the Great and King Frederick William II. They were taken from a locked cabinet on July 16 in a room closed to the public while a wedding was being held at the National Trust-managed stately home.
Detective Constable Ray Swan of the Met's Art and Antiques Unit, said: "The cups and saucers are of significant historical value [and] we believe that whoever took them, specifically targeted these pieces.
"We would ask any dealers, auction houses or collectors that may be offered these items for sale to contact the Met's Arts and Antiques Unit on 020 7230 2150 or email email@example.com."
The cups are painted en grisaille with heavy gilding, flower sprays, finials and branch handles.