A Washington man pleaded guilty in D.C. Superior Court yesterday to three counts of second-degree murder in the March 1981 arson deaths of his three infant children after a firebombing that occurred hours after police had ordered him to stay away from the children and his common-law wife.

Darnell Winfield Jackson, 29, of 52 L Place NW, admitted he threw a flaming can of gasoline through the only window in Rita Elizabeth Fox's room at 214A Morgan St. NW.

The gasoline spread a fatal blanket of flame over their three children -- Darnell, 2; Anita, 1, and Sheila, 2 months.

Nearly five months before the fire, a D.C. Superior Court judge had ordered Jackson, who had lived with Fox for five years, to stay away from the rooming house.

The order came after Fox, who was born partly paralyzed on her left side, complained that Jackson had stabbed her in the back and near the mouth with a butcher knife, and scalded her with grease, according to court records.

On the night of the fire, Fox had called D.C. police when Jackson came to see her and started pounding on her locked door. Officers told him to move on, but he returned a few hours later and started throwing rocks at the window, Fox said in an interview after the incident. Then he threw the flaming can of gasoline.

The incident spurred legislative efforts to better protect battered women. A bill bearing on the subject was passed by City Council, signed by Mayor Marion Barry and is pending in Congress.

The bill, introduced shortly after the fire, makes it easier for battered women -- whether legal spouses or roommates -- to obtain civil protection orders from judges that would be enforced by police officers.

At the hearing yesterday before Chief Judge H. Carl Moultrie I, assistant U.S. Attorney F. Joseph Warin said that if the case went to trial, the prosecutors could produce witnesses who saw Jackson putting gas in an antifreeze can, and who saw him at the home moments before the fire and running from the scene moments later. In addition, Jackson had signed a statement admitting he had tossed the can through the window, Warin said.

Jackson pleaded guilty to three counts of second-degree murder, one charge of assault with intent to kill while armed and arson.

Moultrie ordered Jackson held without bond pending sentencing on Oct. 15.