A consumer hot line service initiated last summer to help callers with changes resulting from deregulation and telephone-related decisions has proved so popular that it has been extended through September 1985, officials said yesterday.

The Washington-based service, Tele-Consumer Hotline Inc., was founded by two consumer groups and provides information to help consumers make choices on long distance, telephone purchases, leasing, repairs, billing and other services. It does not provide long-distance rates or equipment.

Hot line counselors try to "answer all telephone-related questions," said hot line manager Susan Katz. Free fact sheets are also available through the hot line, she said.

The hot line operates between 9 a.m. and 5 p.m. Monday through Friday. The toll free number for callers in Virginia, Maryland and West Virginia is 1-800-332-1124. In the District, the number is 483-4100.

Katz said the hot line, which began operating July 1, was the first of its kind in the nation. An evaluation of the first three months of service, she said, "showed a higher percentage of customer satisfaction with the service and a willingness of consumers to use the hot line again."

Funding for the program, which was founded by the Consumer Federation of America and the Telecommunications Research and Action Center, was provided by local and long-distance telephone companies, including the Chesapeake & Potomac Telephone Co., GTE-Sprint, MCI and AT&T Communications. In addition, the hot line is being publicized by C&P, which is providing the number to customers who ask for more information than the company can provide.

"C&P is restricted from providing information on long-distance companies and equipment vendors since the breakup of the Bell System on Jan. 1, 1984," said C&P consumer affairs manager Rose Wheeler. She said C&P agreed to help finance the hot line because it provides free information to consumers and "treats all the competing companies fairly and equitably."