Glenn said:

So you think a U.S. General has the right -- and should exercise the right -- to defy orders from the Commander-in-Chief whenever he decides on his own, without any court ruling, that the Constitution allows that?

It is not a question of the Constitution. A U.S. General has no constitutional obligation except to support and defend the Constitution. Nothing in the Constitution about obeying orders. In fact, the Nuremberg tribunal established that an officer has a moral obligation to refuse a criminal order. "I was following orders" is not a defense for someone who has a viable alternative to obeying the order. And waging aggressive war is criminal. From Justice Jackson's opening statement at Nuremberg, Nov. 21, 1945:

Any resort to war — any kind of war — is a resort to means that are inherently criminal. War inevitably is a course of killings, assaults, deprivations of liberty and destruction of property. An honestly defensive war is, of course, legal and saves those lawfully conducting it from criminality. But inherently criminal acts cannot be defended by showing that those who committed them were engaged in a war, when war itself is illegal. The very minimum legal consequence of the treaties making aggressive war illegal is to strip those who incite or wage them of every defense the law ever gave, and to leave the war-makers subject to judgment by the usually accepted principles of the law of crimes.

And then Glenn said:

That sounds a lot like the Bush theory of executive power -- he is free to violate Congressional law whenever he decides that the law encroaches on his Constitutional powers, because his ultimate duty is to the Constitution.

That sounds a lot like a straw man argument: First invoking the Constitution where the Constitution is not invokable and then saying it parallels other abuses of the Constitution. Bush's attempts to garner powers not granted to the president by the Constitution while claiming that the Constitution gives him these powers cannot be compared to a US general acting according to international precedents and conventions outside of and without referring to the authority of the Constitution.

And then Glenn said:

Also, the military seems to be saying that they will not participate in an attack on Iran under any circumstances, meaning even with Congressional approval. Do you support that as well?

Circumstances alter cases. It is my opinion, however, that if Congress approved a war of aggression, a general officer would still be within his rights to refuse to participate. This would, of course, get into the territory of his oath to defend the Constitution since the Constitution gives Congress the authority to declare war and says nothing about whether such war is illegal or not. However, through the War Powers Act, Congress has authorized the president to use military force for 60 days without specific congressional approval, and I see no difference between participating in an illegal war started by the president and one authorized by Congress.

And then Glenn said:

What if Congress agrees with the President that we should attack (as they did with Iraq and (I think) as they would do with Iran). Does the General have any options other than to obey or resign?

I'm not sure that Congress (or at least a significant portion of it) agreed that we should attack Iraq. The AUMF was predicated on certain conditions being met that the president had to certify had been met before force could be used. Many in Congress voted approval in order to give the president a credible threat of force in order to compel compliance with UN resolutions and weapons inspections in the face of inflated and distorted information about Iraq's weapons capabilities. That the conditions for the use of force had not been met when the US invaded (despite the president's certification that they had) does not constitute agreeing to attack Iraq. Most of Congress did not realize at this time that Bush lies and that he cannot be trusted with instruments that are worded loosely or vaguely.

As to a general's options other than obey or resign, he can refuse to obey and accept a court martial. Of course, even if acquitted his/her career is over, but it is a principled stand.

He is not a general, but compare the case of 1LT Ehren Watada. He refused to deploy to Iraq with his unit, claiming that the war is illegal. He tried to resign but was not permitted to. He is charged with missing movement (art. 87 UCMJ) which is an open and shut case. No specific intent is required. It is sufficient that your unit was ordered to move and you missed the movement. That's all that has to be proved to convict. However, he is also charged with other offenses which will allow him to argue the legality or otherwise of the war in court. I will be surprised if the Army does not drop these other charges.