After surviving Hurricane Katrina's initial blow, the radio communications system for the New Orleans police and fire departments dissolved as its radio towers lost their backup power generators in the ensuing flood.

Some of the equipment could have been brought back up quickly, except that technicians were blocked from entering the submerged city for three days by state troopers who were themselves struggling with an overwhelmed radio system from a different manufacturer.

"I didn't get a chance to plead my case," said Jan Edwards, service manager for the New Orleans radio system's maker, Tyco International Ltd. subsidiary M/A-Com Inc.

While Edwards and his team were detained on its outskirts, emergency workers inside the city were mostly limited to a handful of CB-like "mutual aid" radio channels, which were quickly overwhelmed.

Four years after the 2001 terror attacks exposed the need for more robust, interconnected communications during such calamities, with nearly a billion dollars appropriated by Congress for the task last year, the United States still lacks uniform systems that can keep all emergency responders in touch.

With regular phone and cellular service knocked out in Katrina's wake — the New Orleans mayor's office had to cobble together an Internet phone link with the outside world — first responders were simply unable to share essential information.

Federal emergency management officials claim they didn't know for days about thousands of people camped out, thirsty and hungry, at the New Orleans convention center. Rescuers in helicopters couldn't talk to crews patrolling in boats. National Guard commanders in Mississippi had to use runners to relay orders.

Yesterday, Democrats on Capitol Hill urged Congress to devote $5 billion a year to upgrading communications equipment for the nation's first-responders. Sen. Mary Landrieu, D-La., said the hurricane exposed a "totally failed communication system."

But many experts say doling out federal money is far from enough. Some advocate creating a national wireless data network — with its own dedicated emergency frequencies — that police, firefighters and all other responders could plug into immediately after a catastrophe.

Such a system wouldn't be immune to damage but could be quickly repaired, says one of its advocates, Reed Hundt, who chaired the Federal Communications Commission from 1993 to 1997.

"You drive the new antenna in on the back of a truck or you carry them in on choppers if they're knocked out or drowned and you can get your network back up in hours," he said in an interview.

Hundt says he has suggested such a project, but the White House has ignored it. The Department of Homeland Security did not return phone calls seeking comment on the issue.

Since 2001, the federal government has given $8.6 billion to states for equipment, first-responder training and disaster exercises. Last year, DHS gave the states $2.1 billion, of which $925 million was spent on or earmarked for communications equipment upgrades.

The department, however, does not tell states what to buy, though it stresses that any system deployed in the field should be able to talk to another agency's system, known as "interoperability" in industry parlance.

Complaints of difficulties in communicating across agencies have been frequent after major disasters — including the Oklahoma City bombing of 1995, the 2001 terror attacks and the Southern California fires of 2003.

Other reasons emergency responders have trouble talking to each other include turf wars among agencies and interference from cell phones on some frequencies.

But one of the biggest hurdles is time and money, said Adrienne Dimopoulos, spokeswoman for Motorola Inc., a longtime public safety radio supplier.

New Orleans bought the M/A-Com system in 1992. Four years later, Louisiana State Police bought its statewide system from Motorola Inc. The two systems have occasionally been bridged to integrate communications during major, planned events such as the 2002 Super Bowl.

The statewide system did stay up after Katrina hit on Aug. 29, while New Orleans' was off the air just a few hours later.