A power failure at the District's emergency communications center disrupted police and fire operations for about an hour yesterday, marking the second time in a year that the system has gone down.

The trouble was compounded by a cascade of equipment problems, including the failure of backup generators, officials said. They said that they did not lose any 911 calls but that workers were forced to dispatch some calls for police from patrol districts.

E. Michael Latessa, director of the center, and other officials said that emergency procedures and quick action prevented the loss of the emergency calls, although some people might have been forced to wait longer than usual for an operator. Fire communications also were disrupted and did not work as efficiently as usual, he said.

The glitches were similar to problems that occurred at the center in July, when a power failure disabled the fire department's radio network and prevented some non-emergency calls from reaching operators.

Yesterday's malfunctions drew criticism from leaders of the city police union, who said they raised questions about the District's ability to respond to a natural disaster or other serious incident.

"This is our Achilles' heel," said Sgt. G.G. Neill, secretary for the D.C. police labor committee in the Fraternal Order of Police Lodge 1. "This is the nation's capital, and the police department can't get radio communications working? Why isn't this problem fixed?"

Power stopped flowing into the Public Safety Communications Center, near Howard University on McMillan Drive NW, about 1:30 p.m., Latessa said.

Within seconds, a backup system that is supposed to switch power to another outside source failed, Latessa said.

The center's backup generators, which are tested every Wednesday, soon kicked in, Latessa said. But after about 20 minutes, Latessa said, the generators began to malfunction and quit.

As emergency batteries began to drain, the center's operations were transferred to a reserve 911 center at police headquarters, Latessa said.

Then, about 40 minutes into the power failure, radio communications in at least three police districts broke down, Latessa said.

Officers were held in reserve at station houses and dispatched on emergency runs by phone calls relayed to the police districts by operators, Latessa said.

Officials were investigating the problems even as they were transferring operations back to the center last night, Latessa said, adding, "This is a big concern to us."

The 911 system was criticized last year after callers were placed on hold during a fatal house fire near Dupont Circle; officials blamed that problem on operators.