US civilian and military leaders are sounding optimistic notes about prospects for scaling back the US presence in Iraq next year as opposition to the war escalates to record levels and congressional demands for troop withdrawals grow louder. Contingency plans for a phased-in withdrawal of troops from Iraq include proposals to postpone further or cancel deployment of a brigade from Fort Riley, Kansas, and an option to post a combat brigade in neighboring Kuwait in case it should be needed, a senior defense official said Tuesday. While military leaders would not confirm the size of any withdrawals, some estimates suggest troop levels could drop to below 100,000 next year, wholly contingent on the progress of the Iraqi government and its security forces. Currently about 155,000 troops are there, higher than earlier levels because of expected violence in the run-up to national elections next month. The official, who would not speak for attribution because no redeployment plans have been completed, said that conditions in Iraq will dictate troop reductions, but stresses on the National Guard and Reserves also are factors.