Jupiter Telecommunications Co. announced Feb. 18 that it has signed a five-year contract with Canada-based digital communication device maker Northern Telecom Japan Inc. for the supply of telecommunications systems to be used in Japan's first cable TV telephone service network.

Jupiter, a multiple-system operator of cable television networks, said the firm plans to initially start service this summer for its cable TV subscribers in Suginami Ward, Tokyo, and branch out to other areas starting in 1998. Northern Telecom was chosen to be the main supplier because of its experience in developing and supplying large numbers of switches to Japanese carriers, including Nippon Telegraph and Telephone Corp., the firm said. It did not say they would be its exclusive supplier.

Jupiter plans to offer the same variety of telephone services NTT does but for 15 percent less, in hopes their service will gradually replace NTT's phones, the officials said. The firm will start with telephone services but will also be testing data transmission over the cable network this year for future expansion of service, according to the officials.

The firm has finished laying down its networks, which are capable of serving up to 1.5 million subscribers within its business area, and nearly 120,000 customers have subscribed. It hopes to expand its network so that the number of potential subscribers can be increased to 3 million by 2000, the officials said.