By Marwa Rashad LONDON (Reuters) – The threat of disruptions to Europe’s gas supply from Russia, in the event the West imposes sanctions if Russia invades Ukraine, has prompted a debate about the need for long-term liquefied natural gas (LNG) contracts. The United States has in recent weeks asked Qatar and other major gas producers whether they can send extra gas to Europe if Russian flows are disrupted, a source said. Some major LNG producers, such as Qatar, and energy companies that have long-term contracts say Europe should rely less on spot contracts and more on long-term contracts for its…