The president's guest house is meant to be fit for a king, but when explosive gas leaked in and a chandelier crashed onto the bed where visiting heads of state sleep, some work was clearly in order.

Six years and $13 million later, Blair House is now a "guest house worthy of this great nation," says Ambassador Selwa Roosevelt, the chief of protocol, who oversaw the restoration.Mikhail Gorbachev couldn't stay there last December for his summit with President Reagan because the house was closed for repairs. But should he return this year he would find a new wing, renovated kitchen, plumbing, fire and safety systems, new electrical heating and air conditioning.

Not a palace, perhaps, but not the dilapidated antique it was in June 1982. Then the house was judged uninhabitable after gas leaked into the boiler room and a chandelier fell on the bed, fortunately then unoccupied.

"We all realized that the house was in very bad shape. All you had to do was look at it," says Roosevelt. "It had a veneer of looking all right because it had a certain warmth and all of that. But the minute you started looking, the rugs were threadbare, the steps were sagging. The plumbing was unbelievable. The kitchens were like kitchens at the turn of the century."

Blair House actually predates the turn of the century, and it is an architectural gem rich in history. It consists of four connecting buildings across from the White House on Pennsylvania Avenue and around the corner on Jackson Place.

The original house dates from 1824 and was long owned by Francis Preston Blair, a member of the powerful, intimate group around President Andrew Jackson that was called the "kitchen cabinet."

Later, the house was a meeting place for leaders on both sides of the conflict that became the Civil War. In a small room to the right of the front door, Col. Robert E. Lee was offered the command of the Union Armies and declined.