After more than a month of darkness, lights were turned on at the Washington Hilton Hotel last night, marking the reopening of one of the city's largest guest facilities after an electrical fire that forced the hotel to close July 27.

Hotel officials yesterday estimated that the fire, which was followed a day later by a second explosion in the hotel's electrical switching vault, cost nearly $6 million in lost business and equipment repairs. But yesterday management was preparing for a full house by this weekend, as trucks unloaded tons of food for the expected guests.

Hotel spokeswoman Renee Subrin said reports of the fire, and suggestions that management did not sound alarms for guests who were in their rooms at the time of the blaze, have not discouraged people from booking rooms there beginning today.

"On the contrary," Subrin said. "People were very understanding, very sympathetic, and we do not feel that it hurt business."

Hundreds of guests with reservations were turned away or placed in other hotels in the city while the 1,154-room Hilton was closed, Subrin said. But 100 of those rooms are expected to be filled tonight, and she said the hotel will be fully booked during the weekend when a computer trade show moves in.

Guests were forced to flee the hotel at 1919 Connecticut Ave. NW when exploding electrical equipment in an underground transformer room adjacent to the complex sparked a fire that went unchecked for nearly two hours. Several guests said that no alarms sounded while the fire burned.

The hotel was fully booked at the time, but only about 100 guests were in their rooms when the fire broke out shortly before 10:30 a.m. The blaze forced the evacuation of 3,800 guests, most of whom were attending a Christian youth convention here. The following day, as workers were trying to fix the electrical system, a second switching apparatus exploded and burned, injuring several persons.

Subrin said workers have since replaced both switching boxes as well as two others that officials feared might have been damaged by intense heat in the fires.

The cause of the two explosions and fires is still under investigation.

Throughout the day yesterday, trucks pulled into the Hilton's loading dock delivering a cornucopia of foodstuffs. Workers unloaded more than two tons of beef tenderloins, veal scallopini, hamburger patties, lamp chops and other meats. There were 1,500 dozen eggs, 2,800 pounds of butter and 1,500 gallons of ice cream headed for the kitchens.

Nearly 600 Hilton employes were laid off when the hotel closed. Many suffered financial hardships over the past month, according to union leaders, but most were expected back on the job today.