A D.C. fire investigator said yesterday that if a sprinkler system had been operating at Kann's department store, Saturday morning's five-alarm blaze, the worst fire in the city in 30 years, would have been easier to contain.

It took about 150 firemen using 50 pieces of equipment 12 hours to bring the fire at Kann's, a Pennyslvania Avenue landmark, under control. The store occupies about three quarters of a city block bounded by Pennsylvania Avenue and D Street between Seventh and Eighth Streets NW. The building had been vacant since 1975, when Kann's went out of business after 82 years.

Investigators said the cause has not been determined and damage estimates were not available yesterday.

D.C. fire investigator Thomas Dodson said the sprinkler system inside the vacant building was shut off several years ago because standing water in the pipes froze during the winter, ruptured and flooded the lower floors.

Dodson said the fire department was notified that the system had been shut off. But firefighters apparently were not aware that the system wasn't working until they tried to feed their own water lines up into the system to start the sprinklers, he said.

"Apparently some sections of pipes had been removed, and the water from the sprinklers never got past the first floor," Dodson said.

Although the blaze had been contained by about 2:30 p.m. Saturday, several fire units maintained an all-night vigil, watching for pockets of smoldering debris inside the structure.Two engine companies continued the vigil all day yesterday.

Dodson said he and a team of four investigators have been hampered in determining the cause of the fire Tons of debris inside the building from the roof and two top floors that collapsed have oobstructed their search for clues.