The Washington Hilton Hotel will be closed until Sept. 1 to replace electrical switching equipment destroyed by two explosions and fires at the 1,154-room facility over the weekend, Hilton officials announced yesterday.

At a news conference, meanwhile, D.C. Fire Chief Theodore Coleman criticized Hilton officials for waiting an hour before ordering an evacuation of hotel guests and employes after the first fire was discovered Saturday in a subbasement electrical vault.

"Surely I would have immediately evacuated the building," Coleman said.

He also faulted the Potomac Electric Power Co. for failing to cut power to the building for 1 1/2 hours, a delay that prevented firefighters from entering the vault to battle the blaze because of the danger of electrocution.

Hotel manager William H. Edwards Jr. has said that he did not clear the building immediately after the blaze erupted because there was no danger the fire would spread beyond the vault and no smoke was seeping into the upper floors of the luxury convention center at Connecticut Avenue and T Street NW.

Pepco spokesman Tom Weele said at the time of the incident Saturday that the power company's emergency crew was working elsewhere and had to complete that work before going to the Hilton. "We got there as fast as we could," Weele said.

The month-long closure of the Hilton is unprecedented for the nationwide chain of 50 hotels, according to hotel spokesman Burt Hoffman, who said the shutdown will cost $2.5 million to $3 million in repairs and lost revenues.

He said the time required to obtain replacement electrical equipment is the cause of the lengthy closing. Two of the hotel's four electrical switchboards were destroyed, one on Saturday and another in a second explosion and fire Sunday that injured nine persons.

The fate of most of the hotel's 800 employes during the closure has not been determined, Hoffman said, adding that some essential workers would be needed in the building.

"Even when a hotel is closed for business there are some operations that have to continue, such as keeping the place clean and general maintenance work," Hoffman said.

He said alternative accommodations have been arranged for all guests and events booked at the Hilton -- the city's second-largest hotel -- during August, including a Knights of Columbus convention scheduled for this weekend.

"We have made arrangements at the Mayflower, the Capital Hilton and other hotels, and so far have been able to accommodate everybody," Hoffman said. A 24-hour communications center has been set up in the Hilton's T Street lobby, and employes are telephoning all persons with reservations to notify them that they will be staying in other hotels, he said.

Coleman said the cause of the two explosions and fires, which forced relocation of nearly 3,800 guests in town for a youth religious conference, has not been determined.

"All we know is what we got hit with, and we don't know why it happened," said the Hilton's spokesman Hoffman. In addition to replacing the damaged equipment, he said, two electrical switchboards not damaged by the fires will be inspected thoroughly.

Coleman said firefighters arriving at the Hilton Saturday entered the hotel and found that the fire was limited to the electrical vault and that no persons were in the area of the fire.

He said firefighters could not determine immediately if electrical transformers containing the deadly PCB chemicals were in the vault, but that, "At no time, I repeat, no time, were our firefighters standing around waiting or hesitating, simply because of the potential involvement and exposure to PCBs." Until Pepco cut power to the vault, firefighters worked to ventilate fumes from the building, helped with the evacuation and performed other tasks, Coleman said.

He said if there had been a life-threatening situation, firefighters would have gone into the area, but that absent that, " . . . I'm not going to subject firefighters to [PCB] hazards."