From the Jerusalem Post:
Regarding the ordination of female rabbis, Lamm said his opposition was "social, not religious."
"Change has to come to religion when feasible, but it should not be rushed. Women have just come into their own from an educational perspective. I would prefer not to have this innovation right now. It is simply too early. What will happen later... I am not a prophet."
This essentially corroborates my own views as referenced in a mildly controversial JTA article a couple of months ago. It is a matter of public policy and not halakha, and - as has been widely discussed in the J-Blogosphere - most Orthodox Rabbis are aware of this fact.