Is it true that to be an effective leader, a public official must maintain the highest ethical and moral standards? The answer to this question might be not. Granted that high ethical and moral standards are to some extent significant to evaluate leaders. Other factors, however, need also to be taken into account to judge whether a leader performs effective or not.
A leader's functions may cover various areas, ranging from political to business to academical and educational fields. Ethical and moral standards are one of the important factors when we see a public leader. Consider a political leader. Ethical and moral standards are necessary since a nation's political leader is representing a nation's image. In which way the leader speaks and behaves may have effect on the nation's citizens and other nations' impressions. One of American president Lincoln is a good example, who use high standards to constrain his action and decision, and has made great contribution to the emancipation of blacks in American history. Consider a business leader, who need to form high moral and ethical standards to do legal trade and compete equally with others. Steve Jobs and Bill Gates are all good leaders with high moral belief. They competes with each other by creating more popular products rather than copying others' ideas. Consider educational leaders, such as a president of a college, who also requires high moral and ethical standards to become the idol or paradigm of all the faculties and students in this college. Finally consider an academic leader in physical area. High moral standards are emphasized in the academic field since stealing others' creativity or idea is treated as the worst thing. Academic leaders are asked to regulate their fellowship to work on their own thoughts and reverence others' achievements.
However, that whether an leader is effective or not cannot be judged only by examining his or her ethical and moral standards. There are many other, maybe more important, factors to determine an effective leader. More generally speaking, an effective leader needs to have their own judgment and determination, as well as his or her ability to understand and cooperate with others, and the responsibility for people and also the admiration by people. Among these standards, high morality and ethos are one aspect to reflect a leader's good personality, which means that the leader will act more fairly when facing controversial situations. Yet, excessive constraints by one's high moral and ethical standards may make a leader estranged from his or her subordinates and people, which may make him or her hard to communicate and coordinate with others.
As we know, the highest morality and ethos are difficult for one person to maintain, especially for some public officials, since they consider more comprehensively and their decision or judgment will influence many people's life or more seriously impact a nation's future. Thus, we could not acquire all public leaders to possess the highest moral or ethical standards. Alexandar the Great is a good example who is unquestionably an effective leader to Macedon. He was undefeated in battle and is considered one of the history's most successful commanders. But he had not maintained the highest moral and ethical standards for his desire of aggression and conflict. 
As a whole, maintaining high ethical and moral standards is to some extent significant to evaluate leaders, while we need to judge a leader from many synthesized facets to determine an effective leader.