BEHIND all the power and prestige of the country's premier industrial group is one company: Tata Sons Ltd. It is this principal holding company that has floated most of the large and profitable Tata companies. A sample: Indian Hotels Company, Tisco, the Tata Power Companies, Tata Chemicals, Telco, and Tata Tea. These companies are supremely important for the group. Reason: not only do they tot up a large chunk of the group's sales and are among the leaders in their businesses, they also generate most of the profits.