By Herbert Lash NEW YORK (Reuters) -The euro fell to a one-month low on Tuesday as tensions between Russia and the West over Ukraine drew investors to the dollar, a day before the Federal Reserve is expected to reveal details on its plans to tighten monetary policy. Western leaders stepped up preparations for any Russian military action in Ukraine while Moscow said it was watching with great concern after 8,500 U.S. troops were put on alert to deploy to Europe in the event of an escalation. Tensions remained high after NATO said on Monday it was putting forces on standby and reinforcing easter…