ONE OF Washington's historic houses, the home where Franklin D. Roosevelt and his large brood lived on R Street NW, is up for sale for $350,000. The former president was assistant secretary of the Navy when the family resided in the R Street house.

It was the Washington residence where FDR lived when he and his wife, Eleanor, are reported to have had many ups and downs over his affair with Mrs. Roosevelt's social secretary, Lucy Mercer. Their son Elliott speaks of the house and those romantic problems in his book about his parents. "The Untold Story." He describes some of the emotional scenes between his parents after Eleanor Roosevelt discovered her husband's infatuation for the charming Mercer.

The spacious - 12 or so bedrooms - house is now the embassy residence of the African nation of Mali. The present ambassador, Ibrahima Sima, finds the parking problems too great in that congested area around 2131 R Street and is looking for property for an embassy residence nearer the suburbs.

The property was sold to Mali in 1961 by television journalist Martha Rountree (Mrs. Oliver M. Presbrey). A pio- neer in electronic journalism, Rountree had already sold her interest in the successful "Meet the Press" when she bought the house in 1958. But she continued to use FDR's old third floor library as her broadcasting studio.

Presbrey says she paid $90,000 for the house in 1958 and and spent $50,000 in improvements. She sold it to the Embassy of Mali in 1961 for about $158,000.

The house is large, with high ceilings. It is regarded as fine for entertaining.

"I loved the house," says Presbery, who now lives Chevy Chase. "The house has a handsome drawing room that was enlarged by an enclosed patio and terrace. I often had 100 guests at a time without any crowding.It was great for entertaining."

Presbrey now heads the Leadership Foundation, which keeps women's clubs around the country informed on public affairs.

The chancery of Mali, across the street at 2130 R Street, will be retained. Only the residence, the old FDR home will be sold. Town & Country is the real estate agent.