WASHINGTON (Reuters) - U.S. President Barack Obama will have a bilateral meeting with Turkish President Tayyip Erdogan during the G20 summit in China next month and is likely to have at least an informal talk with Russia’s Vladimir Putin, the White House said on Monday.   Obama wants to talk with Erdogan about events in Turkey after July’s attempted coup, the military campaign against Islamic State, and how to promote stability in Syria, Deputy National Security Advisor Ben Rhodes told reporters.  The White House said it opposes Turkey’s push into areas in northern Syria controlled by the Syrian Democratic Forces, or SDF, an opposition group the Obama administration supports, as it stands to erode the united front against Islamic State.  The Obama-Erdogan meeting is scheduled for Sunday. It was not certain whether Obama would hold a formal meeting with the Russian president during the G20 summit of the world’s biggest economies, which runs Sept 4-5. But the two leaders often speak on the margins of such summits, Rhodes said.  “We usually try to find an opportunity for the two leaders to try to spend some time together, usually to focus on Syria and Ukraine,” Rhodes said. The United States is at odds with Russia over the eastern Ukraine conflict and Washington and Moscow have struggled to stop fighting in Syria’s civil war. Kremlin spokesman Dmitry Peskov said a meeting between Putin and Obama has not yet been coordinated, Russian RIA news agency reported. “We are ready,” RIA cited Peskov as saying. “But there is no final agreement yet.”  