D.C. arson investigators yesterday sifted through the rubble of the former Nicaraguan embassy here, looking for clues to the cause of a fire that gutted the once elegant building early yesterday morning.

The blaze, which investigators believe was deliberately set, left the uninsured mansion at 3200 Ellicott St. NW a charred hulk that will cost more than $1 million to repair, according to one investigator. The building has been abandoned and partially boarded up since the 1979 overthrow of the Somoza regime in Nicaragua.

Investigators said an empty one-gallon gasoline container was found on the first floor of the mansion and other containers that might have been used to start the fire were found on the 2.1-acre estate just off Connecticut Avenue in upper Northwest Washington.

"There was no question there was a lot of preparation. Considerable time was taken," said Sgt. Walter Franek of the joint D.C. Police-Fire Department arson squad.

Guillermo Sevilla-Sacasa, former Nicaraguan ambassador and once dean of the Washington diplomatic corps, had lived in the mansion for decades, until his eviction in July 1979 by supporters of the victorious Sandinista rebels.

Nicaraguan officials said yesterday the estate, which is appraised at $1.1 million, has been on the market for some time and carried insurance covering only personal injury. The officials said no one has called claiming responsibility for the fire.

They declined to speculate on who might have been responsible. "We have lots of enemies and enough problems without my making such comments," one high-ranking official said, referring to recently deteriorating U.S.-Nicaraguan relations. "That it happened to Nicaragua causes us serious concern," he said.

Nicaraguan officials have asked the State Department for increased protection of embassy personnel and property here. Nicaragua, which has no ambassador currently living here, maintains chancery offices at 1627 New Hampshire Ave. NW.

The spacious grounds behind the Ellicott Street residence appeared unkempt yesterday. The grass was uncut, the swimming pool partially filled with debris and muddy rainwater. Pages from an appointment book dating from the Johnson presidency and apparently belonging to Sevilla-Sacasa's wife, Lillian, list dinners at the White House, receptions for wives of ambassadors, luncheons and social gatherings typical of Sevilla-Sacasa's busy social calendar in prerevolutionary days.

A spokesman for the Nicaraguan embassy said that there have been several buyers interested in the property, including East Germany, which had wanted to use the residence as an office building. That proposal was vetoed by city zoning officials, the spokesman said.

"Most of the value of the property is in the land," the spokesman said, since the building needed extensive renovations by the time Sevilla-Sacasa left and has since deteriorated through abandonment and abuse by vagrants. Nicaraguan officials had not determined yesterday whether they would try to restore the home. One D.C. fire official, noting the extensive damage to the interior and the destroyed roof, said it was unclear whether the building was salvageable.

Many of the prospective buyers appeared interested in either leveling the mansion or converting it into apartment units and subdividing the rest of the property, the spokesman said. Market conditions are such now that it is unlikely it can be sold in any event, he said. One source familiar with the property said the Nicaraguans wanted about $2 million for it.

Neighbors had constantly complained of vagrants who tried to make the mansion their home, Franek said. An elaborate security system apparently was not working, one investigator said, since the electricity and other utilities had long been turned off.