In 1958, when the United States sent its forces to Lebanon during the 1958 Lebanon crisis, Matsudaira considered the move debatable. Although he was prepared to support the resolution, Gunnar Jarring, upon being instructed by Östen Undén, declared that the move by the United States changed the fulfillment conditions for the resolution. Following Jarring's calls for suspending the activities of the UN in Lebanon, the Security Council held the debate until adjourning upon Matsudaira's suggestion. Later that year, Matsudaira served as President of the United Nations Security Council in October. He served in that position again in October 1959.