One official, who spoke on the condition of anonymity because the investigation is continuing, said of the gas line, “I don’t know what’s in this guy’s mind, but it was definitely tampered with.”

Investigators were also seeking to determine whether the furnace and hot water heater had also been tampered with, the official said.

The city’s chief fire marshal, Louis F. Garcia, said the hose had been attached to a valve near the gas meter. “This certainly is against any kind of plumbing code,” he said. “It shouldn’t be there.”

. . .

Chief Garcia said that natural gas reaches the explosive range when it replaces 5 percent to 15 percent of the air in an enclosed space. An explosion can be sparked by anything from a telephone to static electricity.

The portion of the inch-and-a-half hose that was in the basement, which investigators were looking for in the rubble yesterday, was attached to the main gas line before it reached the meter, fire officials said. The gas line leading out of the meter was much smaller in diameter, one utility official said, suggesting that would have speeded the volume of gas escaping into the house.

Chief Garcia said the blast began in the basement, in the front of the house. He said that Dr. Bartha was found on the top of the stairway, on the first floor, directly above where the hose was attached to the gas line. He and other officials said the hose stretched through the basement. By last night Fire Department investigators had determined that it had not reached the furnace at the back wall of the house, though they did not know where it ended, one official said.

But in New York City, and along much of the East Coast, a dwelling jammed rafter-high with junk is referred to by rescue personnel, with dismay and no small degree of respect, as a “Collyers’ Mansion.” As in, primary searches delayed because of Collyers’ Mansion conditions.

The phrase, as many New York history buffs know, refers to the legendary booby-trapped brownstone in Harlem in which the brothers Homer and Langley Collyer were found dead in 1947 amid more than 100 tons of stockpiled possessions, including stacks of phone books, newspapers, tin cans, clocks and a fake two-headed baby in formaldehyde.

The Collyer Mansion is not just a slice of urban lore and a monument to what psychologists now recognize as obsessive-compulsive disorder. It is, in New York, an official term of art, taught in the Fire Academy to cadets learning the potential dangers that can await in burning buildings.

Steven Waddell, of Fairfield, N.J., told The Post from his bed at St. Vincent’s Hospital yesterday evening that he doesn’t remember much, but knows he’s fortunate to be alive.

“I feel like I should be dead now,” he said. “I really didn’t feel like dying that day, I guess.”

Despite lying on the rail for more than two minutes, Waddell only suffered burns to his right elbow and thumb.

“It paralyzed me right away. I tried to pull away from it, but your body doesn’t let you,” he recalled. “I thought I went to hell. It felt like my body was being literally torn apart.”

Before the incident, Waddell had been out for a night of high-voltage drinking with some friends from high school at a bar on Lafayette Street.

Around 2:30 a.m., he and a pal called it quits and walked to the N and R platform to catch the train to his father’s Manhattan apartment.

Woozy with drink, the college senior leaned over the platform’s edge to see if a train was coming and lost his footing, tumbling into the tracks and onto the third rail — which was coursing with 600 volts of electricity.

No one was hurt in the 11:40 p.m. blast outside New York City Bagels on Sixth Avenue between 16th and 17th Streets.