If a person has the opportunity to do the mitzvah of Kiddush Levana and the mitzvah of sefiras ha’omer, which mitzvah should he do first? The issue at hand is the concept of “tadir ush’eino tadir tadir kodem.” If something comes around more often than something else, the priority goes to what comes more often. There is another question as far as how to interpret what is considered more often. Do we measure by the amount of times one does the mitzvah, or do we rather measure the mitzvah by how often we experience this mitzvah throughout the year? On one hand, Sefiras Haomer is done more often since we count for forty-nine days, whereas KiddushLevana is done twelve times a year. On the other hand, Kiddush Levana is applicable every month throughout the whole year, whereas Sefiras Haomer takes place between Pesach and Shavuos.
We can try to bring different proofs to answer the above question. The Aruch Laner in Sukka, daf nun vov, amud alef on Tosfos s.v Ad brings proof that something that is spread out across the year takes precedence over something that is done more times, but in a limited time frame. The Gemara in Shavuos, daf tes, amud alef says that the goats that were brought on Rosh Chodesh are tadir over the goats that were brought during Yom Tov. If you count the goats of Yom Tov, we see that it was brought sixteen times during the seven days of Pesach, one day of Shavuos, and eight days of Sukkos. The Rosh Chodesh goats totaled only twelve, yet the goats of Rosh Chodesh took precedence over the goats of Yom Tov. We see from this that something that took place in a larger time frame on the calendar takes precedence over something done more in count, but in a smaller time frame on the calendar.
The Shaagas Aryeh in siman chof bais discusses a person eating his Shabbos or Yom Tov meal and has two mitzvos to do: the mitzvah of Sefiras Haomer and the mitzvah of Bentching. The person should bentch first and then count Sefiras Haomer. The reason for this is that there are over fifty opportunities for birchas hamazon of Shabbos and Yom Tov, but sefirah occurs only for forty nine days. Birchas hamazon of the weekday are not counted since a person has no requirement to wash during the week. If the statement we said before that something that is spread out in a larger time frame on the calendar is considered tadir, then automatically birchas hamazon should take precedence because it is spread across the calendar. The fact that the Shaagas Aryeh does not use that reasoning seems to prove that tadir is measured in terms or amounts and not by the location across the calendar.
In Shulchan Aruch, siman taf peh tes, seif tes there is a discussion that Kiddush made in shul should be done before Sefiras Haomer. The Magen Avraham in seif koton yud daled explains that this is so because we try to bring in the Shabbos as early as possible. The Teshuvos Yad Eliyahu, siman mem alef asks, why don’t we say the reason is because Kiddush on Shabbos is done more often than Sefiras Haomer? The Teshuvos Divrei Malkiel, chelek alef siman tes zayin answers that the case in discussion was dealing with Kiddush on Yom Tov, which does not come as often. If we say that something that is spread out on the calendar is considered more often, the Kiddush on Yom Tov is spread out from Nissan through Tishrei, whereas sefira is only applicable in Nissan until VovSivan. We could argue that the Kiddush which occurs only three times across the calendar would not be considered more often than forty nine days of the Omer. The same logic may be used when a person forgets vesen tal u’matar and now has to say it in Shema koleinu, the same place where he says Aneinu for a taanis. The Shulchan Aruch in siman kuf yud zayin, seif heh says to say vesen talu’matar first. The Levush in the Pri Megadim explains this is so since vesen tal u’matar is said more often than Aneinu despite the fact that Aneinu may be said across the whole calendar, whereas vesen tal u’matar is said only in the winter. Here too, the disparity of amount of times of vesen tal u’matar is so much greater that we don’t use the fact that it is spread out across the calendar.
Another proof to the other position; that the calendar takes precedence over amount of times, is from the fact that we say the Shir Shel Yom before L’Dovid. The Shir Shel Yom is only said about fifty times a year as each day of the week had its own Perek in Tehillim, yet L’Dovid is said a little over a hundred times. We see from here that the calendar takes precedence over amount of times.
We have brought proof to support both sides of this discussion. If anyone is able to shed some more light on this question, please contact me.