WASHINGTON — Long before the mortgage crisis began rocking Main Street and Wall Street, a top FBI official made a chilling, if little-noticed, prediction: The mortgage business, fueled by low interest rates and soaring house values, was starting to attract shady operators, and billions in losses were possible.

“It has the potential to be an epidemic,” Chris Swecker, the FBI official in charge of criminal investigations, said in September 2004. But, he added reassuringly, the FBI was on the case. “We think we can prevent a problem that could have as much impact as the S&L crisis,” he said.

Today, the damage from the global mortgage meltdown has more than matched that of the savings-and-loan bailouts of the 1980s and early 1990s. By some estimates, it has made that debacle look like chump change. But what is also clear is that the FBI failed to avert a problem it had forecast accurately.

Banks and brokerages have written down more than $300 billion of mortgage-backed securities and other risky investments in the past year or so. Most observers have declared the mess a gross failure of regulation. To be sure, in the run-up to the crisis, market-oriented federal regulators bragged about their hands-off treatment of banks and savings institutions and their executives.

But it wasn’t just regulators who were looking the other way. The Bush administration FBI and Justice Department, which are supposed to police potentially illegal activities by bankers and others, were so focused on national security and other priorities that they paid little attention to white-collar crimes that might have contributed to the lending and securities debacle.

And now that the problems are out in the open, the government’s response strikes some regulators as too little, too late.

Swecker, who retired from the FBI in 2006, declined to comment. But sources familiar with the FBI budget process, who were not authorized to speak publicly about the growing fraud problem, say that he and other FBI criminal investigators sought additional assistance.

They ended up with fewer resources, however.

Last year, the number of agents pursuing mortgage fraud sank to around 100. By comparison, the FBI had about 1,000 agents deployed on banking fraud during the S&L bust of the 1980s and ’90s, said Anthony Adamski, who at the time oversaw financial crimes investigations at the FBI. The bureau says it now has about 200 agents working on mortgage fraud, but critics say the agency might have averted much of the problem had it heeded its own warning.

“The FBI correctly diagnosed that mortgage fraud was epidemic, but it did not come close to meeting its announced goal,” said William K. Black, who was a federal regulator during the S&L crisis and now teaches economics and law at the University of Missouri-Kansas City.

“It used everyday procedures and woefully inadequate resources to deal with an epidemic,” he said. “The approach was certain to bring symbolic prosecutions and strategic defeat.”

FBI officials contend that as house prices were rising several years ago, losses in the mortgage market — and the potential crimes behind them — were not immediately apparent.

Officials said they began approaching mortgage companies and others in an attempt to raise awareness about the growing fraud problem. But the lenders had little incentive to cooperate because they were continuing to make money and, in some cases, were part of the fraud.

“Nobody wanted to listen,” said Sharon Ormsby, the chief of the FBI’s financial crimes section. “We were dealing with the issue as best we could back then.”

Over the past three years, the FBI and other agencies have brought dozens of mortgage-fraud cases. The bureau has rooted out foreclosure rescue schemes in which homeowners are tricked into signing over house deeds only to see the value drained by con artists. Agents have disrupted cases of identity theft in which criminals open — and exhaust — home-equity lines of credit and leaving homeowners stuck with the bills.

Many cases have been relatively small, however, with about half the investigations involved dollar losses of less than $1 million — the size of two or three loans.

But the tepid response also reflects a broad realignment of law-enforcement priorities at the Justice Department, in which mortgage fraud and other white-collar crimes have been subjugated to other Bush administration priorities.

Part of that has reflected the ramp-up in national security and terrorism investigations after the Sept. 11, 2001, attacks. But the administration also has put more support behind efforts against illegal immigration and child pornography.

In a way, the mortgage debacle could not have come on the FBI radar screen at a worse time. Just as Swecker was making his forecast, the FBI, under pressure from Congress and the White House, was transferring hundreds of agents from its criminal investigations unit into its anti-terrorism program. About 2,500 agents doing criminal work — 20 percent or so of the entire force — were affected.

Even as the number of new white-collar cases started declining, the Justice Department pursued some high-profile corporate prosecutions, such as those arising from the collapse of Enron Corp. But some former prosecutors question the administration’s current commitment to pursuing new complicated and high-stakes cases.

“I think most sitting U.S. attorneys now staring at the subprime crisis find scant resources available to pursue sophisticated financial crimes,” said John C. Hueston, a Los Angeles lawyer who was a lead federal prosecutor in the trials of Enron executives Kenneth L. Lay and Jeffrey K. Skilling.

Absent a major shift in priorities and resources, he said, the Justice Department and the FBI figure to continue on their current path of focusing on simple cases “that don’t go to the heart of the problem.”

The FBI says it has 21 open investigations into possible large-scale fraud related to the subprime meltdown. It might be hard to jump-start such probes, though, because delving into the complex financial processes of the mortgage problem could take years.

“I am happy to have investigations going on, but these investigations should have taken place years ago,” said Blair A. Nicholas, a San Diego lawyer representing investors who lost money in the collapse of several subprime mortgage lenders. “They seem to always get involved after the horse has left the barn. It is always cleaning up the mess rather than being proactive.”