Sumner Redstone’s Viacom announced Tuesday that it expects to conduct its planned breakup sooner than initially thought, with the split expected to occur by the end of the year. The company had said it would complete the breakup in the first quarter of 2006.

The split involves creating two separate public companies, with the assets of MTV Networks and Paramount Pictures forming the new Viacom while the assets of CBS, Infinity Broadcasting and Simon & Schuster form CBS Corp.

The breakup is the brainchild of Mr. Redstone, who is looking to jump-start Viacom’s stock price. Investors have lamented that given Viacom’s combination of slow-growth assets such as CBS and Infinity and high-growth properties such as MTV Networks, it has been difficult to figure out whether Viacom is a growth stock or a value stock.

By splitting up the slow-growth and high-growth assets, Mr. Redstone says, he hopes to match the right investors to the right stock.

However, some critics have suggested that the decision is more rooted in Mr. Redstone’s aversion to choosing between his two lieutenants-co-Chief Operating Officers Tom Freston and Leslie Moonves-for his successor.