The debt-collection industry, booming as many Americans struggle to catch up on their payments or walk away from what they owe, was the subject of a record 164,361 complaints through Dec. 8 of this year, according to the Federal Trade Commission. The total is 17% higher than the 140,036 debt-collection complaints the FTC got for all of 2010.

Since the start of this year, though, the FTC has launched just four enforcement actions against debt-collection firms under the primary federal law used to oversee the industry. From 2005 to 2010, the average was two cases a year.

The actions often target companies that are responsible for hundreds, if not thousands, of consumer complaints.

The agency usually goes after debt collectors by filing lawsuits against companies in federal court. Officials also can levy fines and demand that violators reimburse consumers for any money that was obtained illegally.

FTC officials said the small number of enforcement actions against debt collectors is a misleading barometer of its determination to punish violators. J. Reilly Dolan, acting director of the agency’s financial-practices division, said in an interview that the FTC “is cracking down on abusive collection practices and directs its resources to go after some of the largest debt collectors.”

In March, the FTC announced its largest civil penalty against a debt collector in U.S. history. West Asset Management of Omaha, Neb., agreed to pay $2.8 million to settle accusations that included threatening to arrest people who owed money.

West Asset Management, a unit of West Corp., neither admitted nor denied wrongdoing as part of the settlement. The company declined to comment.

Mr. Dolan added in a statement that the FTC is conducting “an inquiry of the debt buying industry” that includes the “quality of information” in lawsuits filed against borrowers.

He declined to be more specific, but law-enforcement officials in several U.S. states have accused some debt buyers of submitting incomplete, sloppy and even fraudulent documents in courts as proof of what a borrower owes. Such companies purchase batches of soured loans in bulk, often for pennies on the dollar, and then try to collect.

Still, J. Howard Beales, who led the FTC’s consumer-protection bureau from 2001 to 2004, said the recent jump in complaints against debt collectors should have triggered an increase in enforcement actions, despite the agency’s limited resources. He now is a marketing and public-policy professor at George Washington University.

The number of debt-collection complaints is surging even though the mountain of overdue bills is shrinking. As of Nov. 30, a total of $96.8 billion in auto loans, credit cards and other unsecured consumer-finance debt was at least 60 days past due, down 19% from $119.5 billion at the end of 2010, according to data from Equifax Inc. and Moody’s Analytics.

Debt collectors are regulated under a patchwork of state and federal laws. U.S. oversight is shared by the FTC and Consumer Financial Protection Bureau.

The Fair Debt Collection Practices Act dictates how debt collectors can contact consumers behind on their bills. Late-night phone calls are illegal, as are physical threats and repeated calls after the collector has been asked to stop calling.

This year’s number of complaints made to the FTC about debt collectors won’t be publicly released until early next year. The agency disclosed the total as of Dec. 8 to The Wall Street Journal following a public-records request. The Journal also obtained individual debt-collection complaints from the FTC.

The tally includes complaints received by mail, phone and online. On the FTC’s home page, a brown button near the top encourages consumers to “Report it to the FTC,” steering them through a form that concludes with: “We have received your complaint.”

People who file complaints with the FTC get a toll-free phone number for follow-up questions and are encouraged to contact state regulators.

The agency compiles information from consumers, law-enforcement officials, the Better Business Bureau and other sources in a database called Consumer Sentinel, which now holds about 6.1 million complaints.

The FTC’s enforcement statistics don’t include actions taken by more than 2,000 other law-enforcement agencies that have access to the Consumer Sentinel database, which purges complaints after five years. Mr. Dolan said those agencies tap the database hundreds of times a week, but the FTC doesn’t keep track of resulting prosecutions, financial penalties or other actions.

Some lawmakers complain that the database is a waste of money. “Collecting information is important,” said Rep. Jo Ann Emerson (R., Mo.), a member of the House Appropriations Committee, in a statement. “But acting on that information is at the heart of the FTC’s responsibility.”

FTC officials wouldn’t comment on the database’s cost. Last year, the FTC spent an estimated $12 million, or about 4% of its operating budget, on items that include the complaint database and National Do Not Call Registry.

Thomas Maronick, a former FTC director who now is a marketing professor at Towson University in Maryland, said he worried when the database was being developed that it would expose the FTC to disappointment. “It creates the impression among consumers that a single complaint will result in regulatory action, but that is not how things work,” Mr. Maronick said.

Mr. Dolan said officials target their enforcement firepower so it will have the maximum impact on consumers and a strong deterrent effect on other debt-collection companies. The FTC also uses the database to spot new problems before they spread more widely, he added.

The biggest subject of complaints so far this year has been Portfolio Recovery Associates Inc., a buyer of distressed consumer debts. The FTC got 2,641 complaints about the Norfolk, Va., company through Nov. 15, a 15% increase from 2,292 during 2010. The company declined to comment.