WASHINGTON, Aug. 9—The United States has expressed to Pakistan concern over the possible effects that any “summary, action” against Sheik Mujib might have on the prospects for peace in East Pakistan, the State Department said today.

John F. King, the department's press officer, said the United States' concern was ex pressed to the Pakistani Government in recent weeks when reports first circulated that Sheik Mujib would be tried.

United States officials emphasized today that the Nixon Administration regarded the matter gravely and would take every opportunity to dissuade Pakistan from drastic action against the leader of the Awami League.