* Studying options to strengthen balance sheet * Asset sales, debt restructuring possible * Submarine, enterprise units under management of CFO * Alcatel exploring pledging of assets to raise debt-source PARIS, Nov 2 (Reuters) - Alcatel-Lucent is considering selling its submarine cable business and a unit that supplies telephone systems to big companies as part of its effort to shore up its balance sheet, according to sources familiar with the matter. The company has yet to hire banks to work on the deals, but a previously announced mid-September move to put the two businesses directly under Chief Financial Executive Paul Tufano is a sign they are candidates for sale, the sources said.