FRANKFURT—The European Central Bank may set policy for a relatively short period at this month’s meeting given heightened uncertainty but should not delay a decision as markets need direction, ECB President Christine Lagarde told Reuters on Friday. Conservative policymakers have called on the ECB to avoid long-term commitments at the Dec. 16 gathering given recent high inflation readings and a resurgence of the coronavirus pandemic, including the emergence of the Omicron variant. Some have even discussed the possibility of pushing out a decision into early 2022, hoping a delay will bring more clarity on growth and inflation—an option Lagarde firmly dismissed on Friday. “There are ways to give clarity without making long-term commitments and I would err on the side of not making (a) very long-term commitment because there is too much uncertainty,” Lagarde said in an interview at  the  Reuters Next conference. “But equally, we need to very clearly …