WASHINGTON — Scams targeting struggling homeowners seeking to stave off foreclosure have skyrocketed, federal officials said yesterday, disclosing that they are investigating more than 2,100 companies and have filed legal actions against four companies.

"The unscrupulous actions of individuals and companies to exploit the misfortune of others is despicable, it's immoral and it's also illegal," said Attorney General Eric Holder, who announced the campaign with Treasury Secretary Timothy Geithner and other federal officials.

Holder said the FBI's "rescue scam" caseload was up 400 percent from five years ago.

The point of the joint effort was to warn homeowners to keep an eye out for potential trouble and to signal to scam artists that "we are united in rooting out foreclosure fraud," said Shaun Donovan, who heads the Department of Housing and Urban Development.

Federal Trade Commission Chairman Jon Leibowitz said that his agency has targeted companies such as the Federal Loan Modification Law Center in Irvine, Calif., that allegedly sought through their names and advertising to suggest they were connected to the government.

The FTC has asked for a court order to halt the marketing tactics of Federal Loan Modification, a private law firm that advertises nationally.

In documents filed in U.S. District Court in Los Angeles, the agency alleged that the firm charged $1,500 to $3,000 in upfront fees for its consumer programs, often promising it could help modify mortgages to make payments more affordable.

"In numerous instances," the agency alleged, consumers were told the firm had "a success rate in the high 90th percentile." But the agency alleged the firm "did not obtain a mortgage loan modification or stop foreclosure in all or virtually all instances."

The managing partner of the firm, Nabile Anz, who also was named as a defendant, said yesterday those allegations were "absolutely untrue."

He said the firm, which went full time into the loan modification business in December, has picked up about 2,500 paying clients a month.

"About 20 percent have gotten loan modifications and their files are closed," Anz said.

The one charge Anz said might "be on the table" for change is the firm name, which the FTC alleged made it sound as if the business is "part of, affiliated with, or endorsed by the United States government or one or more federal government programs."

Anz said that could be remedied. "I don't have a problem in changing that," he said.

One tip-off that an offered service may be a scam is that it asks homeowners to pay upfront fees, officials said at the news conference. They stressed that none of the new programs announced by the Obama administration in recent weeks require any upfront fees.

Given the huge size of the mortgage crisis and the relatively limited resources of state and federal investigators, it was unclear how much effect the new campaign would have on the problem.

But the White House has been looking for ways to demonstrate its concern for the difficulties of struggling homeowners, especially in view of the popular backlash against its massive bank bailout program.

Among the first public events Obama has planned this week after he returns from Europe is one highlighting the number of Americans who have benefited from refinancing their homes at lower interest rates this year.

In many cases, federal officials said, mortgage scams have masqueraded as affiliates of a $75 billion program Obama announced in February to help up to 9 million homeowners avoid foreclosure — except that, unlike the real federal program, they try to collect fees from homeowners in advance.

"These companies are kicking people when they're down," Leibowitz said, "charging enormous up-front fees and sabotaging efforts by homeowners who could be getting help for free."

The agency also sent out warning letters to 71 additional companies that appear to be marketing deceptive loan modification or foreclosure relief plans, Leibowitz said.

Illinois Attorney General Lisa Madigan, a potential gubernatorial or U.S. Senate candidate from Obama's home state, has waged a high-profile campaign against mortgage scams. She attended the news conference to announce civil lawsuits against two Chicago-area companies that have been advertising on local Spanish-language radio stations.

To date, she has brought lawsuits against 24 companies charged with running fraudulent mortgage assistance schemes in Illinois, she said.