(Halacha presented by HaGaon HaRav Shemuel Pihasi Shelit"a)
The Gemara in Masechet Berachot (34) establishes a fundamental rule regarding mistakes made in the text of the Amida prayer: the first three Berachot of the Amida are treated as a single unit. This means that if a person makes a mistake during the first three Berachot and does not catch his mistake right away, he must return to the beginning of the Amida. He may not simply return to the place where he made the mistake, and must instead return to the beginning of the Amida prayer, since the first three Berachot are treated as a single unit. This applies as well to the final three Berachot, and to the middle thirteen Berachot. Each of these three sections of the Amida (the first three Berachot, the middle thirteen Berachot, and the final three Berachot) is regarded as a single unit, and one who makes a mistake must therefore return to the beginning of that section.
One example of this rule is a case of one who during Aseret Yemeh Teshuba (the period from Rosh Hashanah through Yom Kippur) mistakenly concludes the third Beracha with "Ha’Kel Ha’kadosh," instead of "Ha’Melech Ha’kadosh." If he does not catch his mistake immediately, and realizes it only after he had proceeded to the next Beracha, he must return to the beginning of the Amida. He may not return to the third Beracha, and must instead begin the Amida anew.
Interestingly, however, Hacham Ovadia Yosef ruled that this does not apply to a Hazan. Tosafot (commentaries by Medieval French and German scholars), commenting on the Gemara’s rule, relate a story told by the Talmud Yerushalmi of a man named Batiti who was leading the prayer services and, during the recitation of "Ve’ha’ofanim" in the section of Yoser Or, became flustered and could not continue. The person who replaced him as Hazan was instructed to resume the service from precisely the point where Batiti had stopped. Intuitively, we would have expected the replacement to have to begin from the beginning of Yoser Or, since the entire Beracha constitutes a single entity. However, the Talmud Yerushalmi rules that the recitation of "Kadosh Kadosh Kadosh" signifies the beginning of a new unit, and thus the new Hazan could pick up where Batiti had left off – right after "Kadosh Kadosh Kadosh" – without returning to the beginning of the Beracha.
Hacham Ovadia Yosef applies the Yerushalmi’s ruling to the case of a Hazan who, after Nakdishach, recited "Ata Kadosh" and mistakenly concluded the Beracha with "Ha’Kel Ha’kadosh" instead of "Ha’Melech Ha’kadosh." Since the recitation of "Kadosh Kadosh Kadosh" in Nakdishach marks the beginning of a new unit, the Hazan in this case does not have to return to the beginning of the Amida, and instead returns to "Ata Kadosh." Hacham Ovadia cites several earlier authorities who took this position, including the Shulhan Gavo’ah and the Ma’amar Mordechai. This is also the ruling of the Yehuda Ya’ale. Although Rav Shelomo Zalman Auerbach (Israel, 1910-1995) disputed this ruling and refuted the proof from the Talmud Yerushalmi, this is the position taken by numerous Aharonim.
According to the final Halacha, then, a distinction exists between an ordinary individual and the Hazan with regard to "Ha’Melech Ha’kadosh." Generally, one who mistakenly recites "Ha’Kel Ha’kadosh" must return to the beginning of the Amida. In the case of a Hazan, however, since he had recited Nakdishach, he returns to "Ata Kadosh," and not to the beginning of the Amida.
Summary: Generally speaking, if a person during Aseret Yemeh Teshuba mistakenly recited "Ha’Kel Ha’kadosh" instead of "Ha’Melech Ha’kadosh," he must return to the beginning of the Amida. However, if a Hazan made this mistake after Nakdishach in the repetition of the Amida, he returns to "Ata Kadosh," and not to the beginning of the Amida.
