The Federal Trade Commission yesterday announced its first use of a two-year-old authority to collect civil penalties from firms charged with practices found to be unlawful by the agency in prior proceedings.

Under the Magnuson-Moss Act, which took effect Jan. 4, 1975, the FTC may seek penalties of up to $10,000 per violation in commission complaints that hadn't before been named in commission complaints but have "actual knowledge" that their conduct is unlawful.

Yesterday, the FTC said five penalty suits have been filed in federal courts against companies charged with engaging in credit advertising practices that had been found unfair or deceptive and unlawful by the agency in prior proceedings. The suits were filed against:

The Ryland Group, Inc., of Columbia, Md.

Ryan Homes, Inc., of Pittsburgh, Pa.

Forest City Enterprises, Inc., and two subsidiaries, Winslow Homes, Inc. and D.C. Winslow Construction Co., of Cleveland, Ohio.

Seligman & Associates, Inc., and a subsidiary, Mid-States Mortgage Corp., f Southfield, Mich.

Herbert K. Horita Realty, Inc., Honolulu, Hawaii.

Ryland, Ryan, Forest City and Seligman are home builders. Horita is a real estate brokerage agency.

The FTC said that Ryland, Ryan and Horita have agreed to settlements which, if approved by the courts, would require each of them to pay $10,000 in civil penalties and make disclosures required by the Truth in Lending Act when advertising credit terms. They would also be permanently barred from engaging in the challenged practices in the future.

In the suits against Forest City and Seligman, the government has asked the courts to impose penalties, permanently enjoin the firms from engaging in the challenged practices, and order them to pay the cost of the actions.