The three Louisiana visitors seemed official as they made the rounds, chatting with many of the hundreds of hurricane evacuees who sought shelter in Magnolia Center in Laurel, Miss.

Saying they were from the Federal Emergency Management Agency, they took names, Social Security numbers, birth dates and other information, promising to speed up the registration process and, more important, payment of disaster benefits.

The problem was that they weren't from FEMA. They were impersonating FEMA officials to steal personal information, said Carl Monk, chief investigator for the Jones County Sheriff 's Department.

The FEMA scam was one of the first reported targeting Katrina victims. Law enforcement officials around the country are bracing for more in the weeks ahead as fraudsters try to gain financially from the misfortune of others.

One woman complained to federal officials about an e-mail solicitation she received after posting her e-mail address on numerous Web sites, seeking a missing relative. The solicitation was an updated version of the old Nigerian scam, offering a $1,000 donation to "help you get back to your normal life financially from the effects of the Hurricane." The money would be sent in a $4,500 check; the woman first had to wire $3,500 to a Nigerian charity.

Dozens of fraudulent Web sites have appeared, pretending to seek donations for Katrina victims. FBI and state officials have cracked down on many of them.

"We haven't had reports of scams yet, but history tells us we will, as the rebuilding begins," said Chris Bence, a spokesman for the Alabama attorney general's office. Bence should know: Alabama has been hit by three hurricanes in the past 18 months, including Katrina. "I feel confident there will be some enterprising criminals out there trying to obtain financial information from victims, posing perhaps as someone from a bank, credit card company or even a government agency," he said.

Bence said he is also certain there will be plenty of unscrupulous contractors offering to repair damaged property. "They will ask for money up front and then not show up to do the rest of the job."

With so many families forced to move without important financial documents, Federal Trade Commission officials are expecting a rash of complaints about credit scams -- such as promises of instant credit, new credit cards and loans -- even if a consumer has no documentation or a bad credit history. "The pitch is geared to this kind of situation," said Eileen Harrington, deputy director of the FTC's bureau of consumer protection. Most of these schemes ask for payment upfront. "Advance fees are always illegal, always a scam," Harrington said.

Similarly, with the water so polluted, Harrington said she expects to see "water-purification scams making a return," with a lot of unsubstantiated and sometimes false claims being made about products.

The Securities and Exchange Commission is seeing e-mails and faxes touting stocks of companies that stand to benefit from disaster-relief efforts. "The first e-mail began the day after the hurricane" and a steady flow has come in daily, said Susan Ferris Wyderko, director of the agency's office of investor education.

One e-mail promised a 350 percent profit per day. The stock price of one thinly traded home-repair company has jumped in the past week as a result of such solicitations, Wyderko said. She declined to name the company but said that before Katrina, very few shares of the company's stock traded daily. Since the hurricane struck, more than 5 million shares have changed hands, and the price has climbed from mere pennies to more than $3 a share.

"I was not surprised to see these, but I was surprised at how fast they started," Wyderko said.

Even before Katrina hit, Alabama and officials from other states and the federal government were warning area residents to beware of fraud, especially offers from unlicensed contractors and solicitations from independent insurance adjusters who promise to file and win big claims but require payment from the homeowner in advance.

Now, in the face of widespread devastation, some state officials are trying to strengthen their enforcement staffs. Mississippi's attorney general, for example, plans to ask for more funding for criminal investigators. His office is also considering asking for laws to make costly home-repair scams an immediate felony; currently, they are misdemeanors until the third offense, said Grant Hedgepeth, head of the state's consumer protection division.

FEMA spokesman Eugene Kinerney said it is not unusual for "people to pass off as our employees after a disaster." Often, he said, impostors ask for money to file paperwork to obtain benefits. FEMA officials, he said, never ask for money and don't seek out disaster victims but rather wait for them to contact the agency, either by phone or at desks set up in shelters and other places.

Monk first learned about the FEMA impostors when many parts of his county, about 100 miles from the coast, still had no power or water. "We were dealing with disaster stuff, trying to get food, ice and water to people who don't have it. I had to stop and take care of these" phony FEMA agents, Monk said. "They talked the talk, were pretty good con artists," he said. They were discovered when a real FEMA agent came to the shelter.

At a hearing, a judge denied bail for the three accused of being the impostors -- identified as Danielle Ann Doyle, Charles Francis Jr. and Michelle Davis -- and they were held in the county jail.

Staff writer Annys Shin contributed to this report.