Bomb specialists in the U.S. shuddered last week when the Department of Homeland Security quietly issued a warning to police and intelligence agencies, alerting them that it was picking up chatter that terrorists had renewed interest in placing improvised explosive devices (IEDs) in airport luggage.

The shudder was not because the information was new -- but because the experts know how ill-prepared the U.S. is for a potential wave of sophisticated bombs that have been developed over the past decade.

“It is not a matter of if it happens, it is a matter of when, and we just aren’t ready,” a bomb technician told FoxNews.com.

“There have been four attempted IED attacks in the United States this year that we know about,” said Thomas Ruskin, a former New York Police Department counterterror officer, referring to last month's attempted car bombing in Times Square, the failed "underwear bombing" of a plane on Christmas Day and two federal indictments alleging bombing conspiracies.

“[For] the city," he said, "the May 1 Times Square car bomb was a wake-up call. We had to rethink everything. But elsewhere around the country, most cities and states aren’t prepared for bombings, much less the new devices being developed in conflict zones.” Among the new devices that are causing concern are bombs that can be set off remotely, by telephone and radio signals, as well as pressure plate ignitions.

Ruskin said the NYPD relies on its own methods to keep abreast of terror innovations, and it is reaching out to military  experts and trying to upgrade its training and preparedness -- all without help from the Homeland Security Department. “Their priorities can be off base,” he said of HSD. "New York gets shortchanged on Homeland dollars."

Several explosives experts both inside and outside the government, all of whom asked not to be named, painted a picture for Fox News of a nation woefully unprepared to deal with sophisticated IEDs. And much of the blame, they said, lies with DHS's failure to pay greater attention to the way terrorists are most likely to strike.

“We know the preferred weapon will be explosive, so why doesn’t the DHS pay more attention?” one asked.

“For years we have been at the bottom of the food chain,” said another government explosives expert. “Money went to technology that didn’t work, and science that cost too much." he said, pointing to the millions of dollars that were poured into mechanical bomb-sniffers -- with meager results.

"But the basics of training and making first responders aware of IEDs, the things that will really save lives, has gotten the short shrift," he said.

The problem, the experts said, was most obvious at DHS's Office for Bombing Prevention (OBP), which, according to the DHS website, “develops tools to improve national preparedness for bombing threats at all levels.”

The OBP has been largely marginalized, the experts said, even as the threat of domestic bombs has increased over the years. OBP's $12-million-a-year budget hasn’t grown since the DHS was created in 2002, with four staff members. It now has 20 members and it has twice been slated for closure. Outsiders say they have watched the office struggle to keep the nation’s 472 bomb squads and 2800 bomb technicians in the loop.

Shawn Stallworth, commander of Michigan’s state police bomb squad, said the situation has become critical -- especially in the wake of the recent attempted IED attacks.

“We are fighting for things we shouldn’t be fighting for, like equipment and training," he said. "We lack a robust information sharing system, we lack enabling technology, we need up-to-date equipment and training, and it just isn’t coming.”

He said that the problem is that “DHS has invested heavily in detection, [but] it has not devoted enough resources to defeating IEDs that get through.” He added that there is no common standard for proficiency in bomb detection. At the bottom rung, he said, some bomb squads are just part-time operations with basic skills.

“There is an unacceptable disparity of skills and experience among bomb squads around the country,” Stallworth said.

He said the OBP is well respected, but underfunded. “It should be providing intelligence, keeping everyone up to date, R&D, coordination and a number of other things, but it just can’t. We need it.”

The situation is hardly any different at the FBI, where an office called the Joint Program Office for Combating Terrorist Use of Explosives was set up a year ago. Its job, much like OBP’s, is to “get a handle on the myriad federal programs that are addressing the improvised bomb issue,” according to an article in National Defense Magazine. But it still doesn’t have a budget or an office, according to bomb technicians. The FBI is still processing a request for an interview with its chief, Barbara Martinez, who told the magazine “it was a bit of a struggle to get people out of their foxholes to share data.”

A request for an interview with Charles Payne, a former Navy bomb disposal expert who came out of retirement to head the OBP, went unanswered.

Ken Contrata contributed to this story.