Microsoft has joined with MCI and British Telecom to sell a package of Internet services and software to multinational companies, offering them one-stop shopping for linking far-flung computer networks. Some industry analysts said the alliance apparently will offer the first all-inclusive package of telecommunications and software services for international companies seeking to set up private Internets. Up to now, companies setting up so-called Intranets had to shop separately for access lines needed to transmit information between global offices. The alliance will continue even if BT's $20.8-billion takeover of MCI, announced Nov. 3, is not completed. The new services will be sold through Concert, a joint venture of BT and MCI.