The State Department wants to use a 40-room Georgetown mansion as a temporary residence for visiting heads of foreign governments while Blair House, the nation's traditional guest house, is undergoing extensive renovations.

James Whitlock, the General Services Administration's assistant regional administrator for public buildings and real estate, said State Department officials called his office last week and asked him to negotiate a lease for the mansion at 3014 N St. NW., which dates to 1799 and is owned by real estate broker Vicki Bagley.

Bagley, who purchased the residence in July 1976, said representatives from State had looked at several properties in the area and "they had decided mine would be best because of the space, and it has a tennis court. A lot of the visitors apparently want to play tennis."

She said she was told the residence might be needed for up to four years, possibly beginning Feb. 1.

State Department officials said that because no lease has been signed, the selection of a temporary residence is not yet final.

State has been housing foreign leaders in various Washington hotels since late June, after a chandelier in the master bedroom of the 115-room Blair House came crashing down onto an unoccupied bed.

Whitlock said he understood that the department's Office of Protocol wanted a house for the dignitaries for "mostly security reasons."

Although the Bagley house is only a block from busy M Street, it offers seclusion and tranquility. The two-story house, which has no front yard, is entered directly from the sidewalk. It has a large side garden and a large back yard, sloping down to the tennis court. The grounds are surrounded by a high brick wall overhung with magnolia trees.

Bagley said that if the lease is successfully negotiated, she and her family will move into a guest house on the grounds.

Protection of dignitaries might mean that sometimes no parking would be allowed on the block between 30th and 31st streets, said D.C. police Capt. William Riley.

The central section of the house was built in 1799. Robert Todd Lincoln, son of President Lincoln, purchased the house in 1918 and enlarged it. He lived there until his death in 1926.