Nova Real Estate Investment Trust President William S. Corish and executive vice president Darrell Armstrong have resigned effective Dec. 31.

Corish and Armstrong both have been with Nova and on leave from First Virginia Banks Inc. since 1973. First Virginia organized Nova under the name First Virginia Real Estate and Investment Trust in 1972 and managed the Falls Church REIT under the name First Advisers until 1976.

Corish and Armstrong were officers of First Advisers and were appointed officers of the REIT in 1976 when First Virginia stopped managing it. The name change to Nova came in 1980.

Corish and Armstrong are the only two First Virginia Bank officers still with Nova.

Nova, a publicly held company, also is involved in a merger proposal process with another REIT, Parkway Co., of Jackson, Miss. Parkway has offered to exchange one share of Parkway stock for each 1.9 shares of Nova. Nova stock traded last week at 5 7/8 and Parkway at 13 1/4.

Parkway already owns 32 percent of Nova after acquiring options for Nova shares from Westport Real Estate Investment Trust of Connecticut. Westport earlier made an attempt to acquire the local REIT, which has assets of $23.5 million.

Armstrong said he expects the merger to go through, and that the officers' return to First Virginia Banks is due to the changing real estate market rather than the proposed merger.

Charles Hurt, a Nova trustee, has been named president effective Jan. 1.

Nova emerged from Chapter 11 of the federal bankruptcy code last March. It had filed for reorganization in 1980 when it was unable to pay $17 million in debts.