The Washington Hilton Hotel, dark and nearly vacant since two explosions during the weekend forced its shutdown, will remain closed "for the next several days," officials announced yesterday, as investigations continued to determine the cause of the blasts.

Officials estimated yesterday that the damage and guest relocation had cost about $2.5 million since electrical switching apparatus exploded and burned twice over the weekend, forcing the sold-out hotel at Connecticut Avenue and T Street NW to close. Each day the hotel remains closed costs the company about $80,000 in lost revenues, according to spokesman Burt Hoffman. More than 650 guests expected to check in through Wednesday have been relocated, officials said.

On Sunday, electrical apparatus in the hotel's underground equipment room exploded and burned, injuring at least nine persons, most of them electricians trying to repair damage caused Saturday by a similar incident. Saturday's explosion caused a three-alarm fire in the underground room and guests were evacuated.

The 1,154-room hotel was booked during the weekend with about 3,800 participants in a religious conference for youth at the Washington Convention Center. Only about 100 guests were in the hotel Saturday when the first explosion occurred, officials said.

Yesterday, busloads of teen-agers, who had been relocated to more than 20 hotels in the past two days, trooped back to the Hilton to pick up their belongings. Most had gone for three days without a change of clothes while they attended the Youth Congress '85 convention.

"It's like a ghost hotel," said 16-year-old Aunicia Bergeron as she came out of the lobby, a tennis racket in hand. Bergeron and two friends, all from Houston, said the hotel was "all dark and empty."

They had climbed stairs lit by makeshift lights powered by special generators. The hallways in the 12-story hotel were monitored by convention staffers holding flashlights.

On the way out, the teen-agers picked up box lunches of ham-and-Swiss cheese sandwiches and chocolate chip cookies, courtesy of the Hilton, which also picked up the tab for their rooms, food and telephone calls since Saturday's relocation.

Meanwhile, officials from the D.C. Fire Department, Pepco and Hilton engineers and other officials from here and around the country worked to determine the cause of the explosions, according to Hilton spokeswoman Renee Subrin. Fire department officials said they hoped to announce preliminary findings today.

About 800 hotel employes were told to stay home yesterday and line employes were asked not to report to work today . They are to call the hotel after 6 tonight to find out when they should report to work.