Reacting to both the threat of competition and the increasing demand for more sophisticated telecommunications capabilities, Intelsat, the international satellite consortium, tomorrow will launch a new international business satellite service.

The new service, called Intelsat Business Service, will be capable of carrying phone calls, television programs, computer communications, facsimiles of documents and electronic mail. Designed to be accessible to customers who have their own satellite earth stations, the system will give Intelsat a degree of flexibility "it has never had before," according to one New York-based analyst.

International banks, shipping firms and other multinational companies could set up their own data and voice communications networks under the IBS structure.

The move into business services by Intelsat--a global consortium of government postal, telephone and telecommunications agencies with headquarters in Washington--is seen as an attempt to head off potential competition from private companies.

Only a few months ago, Orion Satellite Corp., of Washington, announced its intent to provide satellite business services to "complement" Intelsat's existing international network. Because of technical shortcomings, Intelsat's satellite system cannot handle most of the needs of international business.

Intelsat's business satellite plan "appears to be a response to Orion and it is clear that the user community has already benefitted from the Orion proposal as a result of this action," said Thomas K. McKnight, Orion's president.

According to Intelsat, the consortium had been planning its business service for several months before the Orion proposal was announced.

More recently, International Satellite Inc., a company mainly owned by TRT Communications Inc., asked the Federal Communications Commission to allow it to provide international satellite business services.

This specter of private sector competition has provoked condemnation from Intelsat as well as an exchange of letters with the State Department, which currently has a task force under way to see if such private carriers would violate Intelsat treaties. The State Department is expected to release its report shortly.

The Communications Satellite Corp.--the United States' signatory of the treaties and this country's representative to Intelsat--has also opposed the applications filed by the potential competitors.

Intelsat estimates that it will cost roughly $92 million to modify its existing satellite network to accommodate business customers

A spokesman concedes that "we were not unaware" of the potential competition when the proposal was filed.