In the United States, the Secretary of Defense just lifted the ban on women in combat. Many Christians seem to oppose this idea and believe that women should not be put in combat.
What is the biblical basis or precedent for this position?
If we go by direct statement, no, the Bible never explicitly states women should serve in active combat. However, as Affable points out, there are plenty of things Scripture doesn't condemn directly that we can assume are wrong by using principles based on extrapolation of direct statements and precedent, in a legal sense. And since the question asked "or precedent", here's one:
For this question, we can look to precedent in that nowhere in Scripture were women appointed to fight in battle. Only men are chosen for battle in Scripture:
This article lists several other hints that apply. One example:
Of course, these aren't direct statements, and it's possible, and even easy to mistake what's said when we try to "read between the lines", so not everyone is going to agree with the conclusion that it's contrary to Biblical principles to send women to war. I'm simply presenting the above, not arguing for or against it.
Just because there is no explicit prohibition on a thing does not mean that the Bible "endorses it."
There is, for example, to the best of my knowledge, no biblical prohibition cannibalism. Possibly it wouldn't fall under definition of kosher, but it is at best ambiguous! In spite of this, the author of the text rightfully expects that the reader is revolted when, (in 2 Kings 6:24-33), during a siege, two women concoct a plan to eat their children. When the second woman reneges and the first brings it before the King, the King rends his garments to show how he too understands how appalling this situation is. That, even in the absence, of an explicit prohibition in the Torah.
Likewise, the idea of women in combat would have simply been so outrageous as to not need explicit mention. Women simply did not fight* or if they did, something was wrong.
This is not to say that every Jewish custom is somehow holy - but "unthinkable" things don't need explicit mention in a contract between two parties - which is what the Old Testament laws were.
*But back to that "women didn't fight." There are two notable exceptions to that rule, but both fall into the category of 'the exception that proves the rule':
In the apocraphyal book of Judith, for example, Judith uses sex and cunning to murder Holofernes, the invading general. Scholars all agree, this fictional tale was written, in many ways, for its shock value. Like David defeating Goliath, this story simply assumes the incongruity of the weak defeating the strong in combat, leaving the reader to marvel at the tables being so turned.
2. Deborah and Barak
Within canonical Scripture, however, the most important story to remember is that of Deborah and Barak (no relation to the current President). Here, like in most of Judges, the Children of Israel have been beset by the enemy for their wickedness, and must now rise up and defeat the enemy. The chosen leader, however, is too reluctant. (Yeah, it really is a different Barak!) He demands that Deborah - the woman God sent to encourage Barak, must accompany him and assist in leading.
Now, on the face of it, you might say: Hey! See - a Woman fighting in combat! The precendent is not only absent, but wrong!
But here's the rub - God (and Deborah) bring judgement against Barak for his lack of cohones. The author writes:
That Barak would have no honor from this battle is quite the indictment. The assumption that a woman should not be in battle is so implicit as to be laughable.
Women encourage, Men fight. That's the model. Are there exceptions? TO be sure - but the Bible is clear its not the model to follow.
I don't think the Bible mention about these. But if the Government make rules, then I think we should follow it unless it is a sin.