(Excuse the delay -- I thought this had already been sent out! -MK)

(a) An "Ika d'Amri" does not necessarily mean that the gemara is changing from its first opinion . It is only a different tradition of what the person actually said. And indeed in this case Rashi seems to have understood both answers to mean the same thing.

The Gevuras Ari, though, explains Rav Elazar's intent in the first version, "Look at the Birah," to coincide with Rashi's explanation. The earlier generations must have been greater then the later, because their temple was rebuilt while ours was not. However he provides an alternative explanation for the second version of Rav Elazar's answer "The Birah is your witness." He explains, the earlier generations must have been greater than the later, because the destruction of their temple was only a partial destruction. Only the mortar was removed from between the stones. While the destruction of the second temple was a total destruction, the very walls were torn down.

(b) As for your second question, that it seems that Rav Yochanan here contradicts his opinion of the meaning of "Birah" on 2A, this too is explained by the Gevuras Ari. He says, Rav Yochanan also agrees that "Birah" refers to the Bais Hamikdosh. The Pasuk in Divrei Hayamim (brought on 2A) outright refers to the Bais Hamikdosh as "Birah". However, he holds that the Kohain who burns the Parah Adumah did not have to be secluded in the Bais Hamikdosh, but could have been placed anywhere on the Temple Mount. Therefore the word "Birah" in the Mishnah in Parah cited earlier (2a) must mean something else.

D. Schloss