MCI Communications Corp. announced Tuesday that it would spend more than $ 20 billion to update its long-distance network to handle the most advanced computer, telephone or television systems and expand access to the Internet, the world’s most extensive computer network.It also said it would spend $ 2 billion creating local phone service in major metropolitan areas. The long-distance project will be called network MCI and use fiber-optic technology known as Sonet, which moves data 15 times faster than any other wire technology now available, MCI said. Sonet, which stands for synchronous optical network, has already been used in half of MCI’s network, said MCI chairman/CEO Bert Roberts. It will be available throughout the company’s domestic network by the end of 1994 and on international routes across the Atlantic and Pacific oceans by 1995. MCI also announced creation of MCI Metro, a wholly owned subsidiary that will invest in switching equipment needed to provide local phone service without going through one of the regional Bell systems.