Harvard economist Greg Mankiw notes the mounting evidence that conservatives are underrepresented in academia, and suggests a possible remedy (without necessarily endorsing it):

Question to think about: If right-wingers are underrepresented in universities relative to the population and discriminated against by the left-wing majority, as Larry [Summers] suggests, should there be affirmative action for right-leaning academics? It seems that, on principle, those on the left (who favor affirmative action to promote diversity and correct past injustice) should endorse such a university policy, and those on the right (who more often oppose affirmative action) would be against.

The underrepresentation of conservatives (and, I would add, libertarians) is almost certainly not all due to ideological discrimination. But evidence suggests that discrimination is probably at least a part of the story. In this excellent Econlog post, economist Bryan Caplan explained why ideological discrimination is more likely to flourish in academia than in most other employment markets. Even aside from discrimination, the ideological homogeneity of much of academia causes a variety of problems, such as reducing the diversity of ideas reflected in research, skewing teaching agendas, and generating the sorts of "groupthink" pathologies to which ideologically homogenous groups are prone.

However, whether or not the discrimination is the cause of the problem, affirmative action for conservative academics (or libertarian ones) is a poor solution. Among other things, it would require universities to define who counts as a "conservative" for affirmative action purpose, a task that they aren't likely to do well. Affirmative action for conservatives would also give job candidates an incentive to engage in deception about their views in the hopes of gaining professional advancement. Moreover, conservative professors hired on an affirmative basis despite inferior qualifications would find it difficult to get their ideas taken seriously by colleagues and students. They might therefore be unable to make a meaningful contribution to academic debate - the very reason why we want to promote ideological diversity in hiring to begin with.