Let me apologize if the following material seems obtusely worded. Some rabbis have a serious problem expressing coherent thoughts that appeal to common sense. Clearly, some of our ancestors were lacking in this department. The Talmudic style of reasoning called, “pilpul” (“peppered” didactic reasoning) can appeal to the inner sophist we all have. At times, I like to refer to this style of argumentation as, “rabbinicspeak,” and to understand or argue with it, you have to almost think like a mental contortionist.
Continuing with our last thought, how could Deborah in the Bible (Judg. 4:4) serve as a judge, according to the Talmudic and medieval rabbis? The 13th century of scholars known as the Tosfot, try to make sense of the problem posed. To their credit, Tosfot offers at least adds fluidity to much of its interpretation; they are a lot like the girl with the curl, when they are good . . . you know the rest of the story. The same may be said of the Tosfot interpretations.
Ba’ale Tosfot discuss the problem from a variety of perspectives:
A. One answer proposed suggests that that Deborah was a judge because her community accepted her. Tosfot also admits that a woman is considered to be an equal in every matter of jurisprudence, except when it comes to serving as a witness. 
B. The Jerusalem Talmud rules that a woman is not allowed to act as a judge ; the case of Deborah is the exception–and certainly not the norm. Deborah was chosen by virtue of the Shekhinah resting upon her.
C. Alternatively, one may accept a woman to serve as a judge, just like two litigants may accept a relative to serve as a judge–provided each party agrees. 
D. Some scholars say that Deborah could only “teach,” but she could not render legal decisions–only men could do that.
In the interest of brevity and clarity: Explanation A strongly supports the idea that a woman may be accepted as a spiritual leader by the community. By the same token there is certainly no violation of “modesty laws,” just like the modesty issue never played a role in the narrative of Deborah. She unabashedly taught Torah and functioned like a judge in every respect.
With respect to the third answer, we discover a view that is similar in substance to the first opinion, but it is somewhat similar to the second view as well. While a woman may not technically be “kosher” as a judge, if she is competent and the people wish to accept her–despite the limitations of gender, a community has every right to accept her–provided she has a strong mandate from the community empowering her to lead.
This is the liberal approach of Rabbi Avi Weiss, which I wholeheartedly support.
Understanding the Conservative View of the Haredim and RCA
It is not hard to see where Rabbis Shafran and Pruzhansky derive their point of view–it is primarily from the Jerusalem Talmud, as well as those scholars who have subsequently followed in its footsteps. They would argue that Deborah is the only woman to function as a judge in the Bible. Centuries of Jewish tradition, since early rabbinic times, certainly (but unfortunately) supports that kind of narrow interpretation. Besides, who says the Jerusalem Talmud is necessarily correct? The last time I checked, nobody in the Talmud ever said that the Sages were infallible.
What About Option D?
Option D does not have even the flimsiest bit of support from the Tanakh; one would have to redefine the verb שֹׁפְטָה (šöpta) in a way that radically different from any other usage found in the Tanakh. Ordinarily, a šofate (judge) decides cases that come before his attention (Exod. 21:31; Deut. 25:1; Josh. 20:6). Thus young King Solomon, e.g., asked God for understanding that he might “hear mishpat”- and a case is shortly brought before him to decide (1Kgs 3:11). The language of the text indicates that Deborah acted no differently than any other male judge before or after her. For this reason, we must reject Tosfot’s reasoning. If anything, Tosfot’s argument here proves the exact opposite.
One More Point . . .
The Mishnah clearly states in “Whoever is eligible to act as a judge is also eligible to act as a witness; however, one may be eligible to act as a witness, but not be eligible to serve as a judge.” A woman really does not fall into the Mishnaic category, which only speaks about someone who can be both a witness and a judge. A woman may serve as a judge, but she cannot serve as a witness. Her exclusion from being a witness does not necessarily exclude her from serving as a judge at all–the Mishnah did not specifically address this kind of case scenario. One suspects the reason why the Mishnah never excluded a woman as a judge is precisely because Deborah functioned as a judge.
For the Mishnaic framers, this was really a no-brainer.
A Possible Compromise for Rabbi Avi Weiss
As a compromise, I think Rabbi Avi Weiss ought to consider ordaining Rabba Hurwitz to serve an exclusively female congregation for the time being. This way, there will be no issue of “modesty,” since it is an exclusive female congregation. Secondly, since the women will have accepted her as a rabbinit (female rabbi), there will be no violation of Jewish law as specified by the sources of A and C, but not B (but possibly D, in a limited sense).
The absence of unanimity should not be a cause for alarm to the Modern Orthodox community, since Halacha has seldom ever been unanimous in its thinking and redefinition. Indeed, there are numerous other rabbinic passages we can look at, but I believe we have demonstrated that Halacha is by no means a monolithic process; social issues do impact a religious and halachic community, as we have mentioned above in the case of woman’s suffrage. I suspect that had Rabbis Shafran and Pruzanski lived during the first part of the 20th century, these men would have opposed women’s suffrage for the same reasons they oppose female rabbis.
I dare any Haredi or RCA rabbi to explain: Why can women vote, serve as supervisors in Kashrut, answer Halachic questions with respect to the Jewish family purity laws, serve as attorneys in the most Haredi rabbinical courts in Israel, but not serve as women rabbis?
Inquiring minds really want to know.
Latest word (March 12, 2010)
The leadership of the Rabbinical Council of America and Rabbi Avi Weiss have apparently reached agreement that Rabbi Weiss would no longer confer the title of “Rabba” upon graduates of his women’s seminary, but rather the title “Maharat.” This superficial move does not in any way change the position of the Moetzes Gedolei HaTorah that placing women in traditional rabbinic positions departs from the Jewish mesorah, and that any congregation with a woman in such a position cannot call itself Orthodox.
 BT Nidah 50a, Tosfot, s.v., כל הכשר לדון כשר להעיד, cf. BT Bava Kama 15a.
 ירושלמי סנהדרין פ”ג ה”ט; טוש”ע חו”מ ז ד
 תוס’ ב”ק טו א, ועי’ ירושלמי יומא פ”ו ה”א ותוס’ נדה נ א ומהרש”א ומהר”ם שם בפי’ הירושלמי, ועי’ תומים סי’ ז ס”ק ה.
.חי’ הר”ן שבועות ל א, וע”ע בית דין שכל הפסולים כשרים לדון כשבעלי הדינים קבלו עליהם
 כל הכשר לדון כשר להעיד– תוספות מסכת נדה דף נ עמוד א