The Chazan leading the services is required to call the Kohanim for Birkat Kohanim and dictate to them the words of the Beracha. If the Chazan is a Kohen, then somebody else from the congregation is invited to call the Kohanim and dictate the words in place of the Chazan.
The question was asked whether a Chazan who is not a Kohen has the option of inviting somebody else to lead Birkat Kohanim in his stead. This question arises occasionally on Shabbat or Yom Tov, or when a special event is held in the synagogue, and the congregation would like to have somebody with a melodious voice lead the Birkat Kohanim service in honor of the special occasion. Is this permissible, or does the Chazan himself bear a personal obligation to lead Birkat Kohanim?
Rabbi Chayim Palachi (Izmir, Turkey, 19th century) addresses this question in his work of responsa Lev Chayim (3:8), and he concludes that it is improper for a Chazan who is not a Kohen to invite somebody else to lead Birkat Kohanim. Nevertheless, in his work Kaf Ha'chayim (15:65), Rabbi Chayim Palachi writes that if the Chazan feels tired or frail, then he may, indeed, invite somebody else to lead the Birkat Kohanim service in his stead. This position also appears in a responsum of the Geonim (cited in Shaarei Teshuva 177), and the work Ma'aseh Avraham records that this was the practice among the Jewish communities of Portugal.
Chacham Ovadia Yosef, in his work Yechaveh Da'at (4:10), extends this ruling to the cases described above, where a congregation wishes to invite somebody with a melodious voice to lead the Birkat Kohanim service in honor of a special occasion. He writes that although it is certainly preferable for the Chazan himself to lead Birkat Kohanim, nevertheless those communities who allow inviting somebody else to take the Chazan's place for this service have a reliable basis for this practice. He concludes, "Let Israel be; if they are not prophets, then at least they are children of prophets." Meaning, if over the years such a custom has developed, then we may assume it was done under the guidance of competent authorities of Halacha.
Summary: Preferably, if the Chazan is not a Kohen, he should personally lead the Birkat Kohanim service rather than invite somebody else to do so. Nevertheless, if he feels weak, he may ask another person (who is not a Kohen) to lead this service, and communities that have the practice of inviting somebody else to lead Birkat Kohanim in honor of special occasions may continue this practice.
