The European Commission's review of the merger of WorldCom Inc. and Sprint Corp. enters its decisive phase this week, as the companies make last-ditch efforts to stop the $115-billion deal from being blocked. Competition experts from the 15 European Union states broadly backed EU Competition Commissioner Mario Monti's draft decision to stop the merger in its present form at a meeting on Thursday, an EU source said. But the source said this did not necessarily mean the merger was dead. Monti is in the United States today for a long-scheduled meeting where the merger case has taken center stage. EU officials are concerned that the merger could stifle competition in the fast-growing Internet industry. But WorldCom and Sprint have stepped up intense efforts to appease competition concerns. WorldCom has agreed to sell Sprint's Internet backbone, and industry sources say it may also shed Sprint's long-distance phone business in an effort to save the deal. The final decision in Europe is due July 5.