BRUSSELS—European officials are scrambling to lock down energy supplies they would need to keep their economies churning if hostilities around Ukraine imperil natural gas piped from Russia, and have turned to the U.S. for help finding backup sources beyond Moscow’s control.

In recent weeks, as Russia has positioned more than 100,000 troops near Ukraine, European Union energy officials have huddled with U.S. counterparts and are jetting to gas producers including Azerbaijan and Qatar to hunt for fallback sources.