Four fires that authorities say were deliberately set caused an estimated $50,000 in damage at the Nicaraguan Embassy early yesterday morning, and embassy officials later blamed the Reagan administration's "aggressive rhetoric" for provoking the arson attack.

The fires, which were in two small bathrooms and anterooms off the embassy's circular lobby, were discovered by embassy employes shortly after 4:30 a.m., according to D.C. fire officials and the FBI. There were no injuries to three employes who were inside the embassy at the time of the fire, but one firefighter suffered a minor eye injury, a fire spokesman said.

Fire and police officials said the embassy, at 1627 New Hampshire Ave. NW, was broken into and that the fires were set by igniting towels and a chair. An FBI spokesman said officials were awaiting further test results to determine the exact cause of the fire.

"The Embassy of Nicaragua is concerned that the baseless and hostile rhetoric against our government could have stimulated this criminal act," embassy officials said in a statement released late yesterday afternoon.

Earlier, embassy press officer Sarali Porta called the fires "a direct result of the high level of rhetoric of the Reagan administration . . . . Aggressive rhetoric always stimulates this kind of action."

President Reagan has frequently denounced the Sandinista government in Nicaragua and advocates U.S. aid to rebel Contras trying to overthrow it. But on Capitol Hill yesterday, Elliott Abrams, assistant secretary of state for human rights, condemned such attacks, including the killing of six Americans in El Salvador Wednesday.

Porta said no group or individual had claimed responsibility for the attack, but that the embassy had received several "strange" calls Wednesday night from people who she said hung up when the phone was answered.

The fires, according to the embassy, caused extensive damage to the lobby area and two bathrooms and destroyed the embassy's switchboard.

Porta initially speculated that a Molotov cocktail had been thrown into the embassy, but fire officials discounted that, saying pieces of cloth were probably set ablaze and tossed inside. A glass door in the front was kicked in, according to police, and an outer metal door was unlocked.

This is the second attack in two weeks on a Nicaraguan Embassy, Porta said. Its embassy in Costa Rica was attacked last week in San Jose by a group that threw stones and broke windows.

The FBI said its investigation into the arson was continuing, and embassy officials said they were increasing security.