The Federal Trade Commission said yesterday it has received a growing number of complaints about debt collection practices but added that the problem is far more serious than even those numbers indicate.

These complaints "represent a relatively small percentage of those consumers who experience improper collection practices," the FTC said in a report to Congress. According to information from state and local consumer protection agencies, complaints to the FTC reflect only a fraction of the problem, the report said.

The number of debt collection complaints to the FTC increased 4 percent in 1984 compared with the year before, an FTC spokeswoman said. She added that the total number was not available, however.

The FTC is primarily responsible for enforcing the Fair Debt Collection Practices Act, which prohibits collectors from acting abusively. Alleged violations of the act, described in complaints to the FTC, include:

* Abusive telephone calls, including the use of profanity, obscenities and racial and ethnic slurs.

* False or misleading threats about what might happen if a debt is not paid.

* Unauthorized contacts about a debt to third parties, such as employers, relatives, neighbors or friends.

* Refusal by debt collectors to verify debts that are disputed by consumers.

The FTC is combating such actions through a combination of education and litigation, the report said.