GEN Petraeus' nomination hearing, at which he was unanimously confirmed as the senior field commander in Iraq (4-star commander Multinational Force-Iraq), seems to be getting very little attention, in that he may well have made a completely Consitutional end run around Administration spin control. During the hearings, presumably attended by at least part of his chain of command, he volunteered to keep Congress briefed, frequently (biweekly was mentioned), and to listen to Congressional input. There are additional twists both in comments by GEN Abizaid, retiring head of Central Command, and in the upcoming confirmation of ADM Fallon as the new CENTCOM.
Racking my memory of US politicomilitary history, I cannot remember another field commander that, prior to taking command, established a friendly and direct consultative process with Congress. As far as I can tell, everything he promised is completely legal. It doesn't violate Goldwater-Nichols, since he still will report through CENTCOM to NCA. Goldwater-Nichols establishes the Chairman of the JCS as the principal military advisor to the President, Secretary of Defense, and National Security Council. It says nothing about advising or not advising Congress.
Petraeus' chain of command could certainly order him not to speak to Congress. Given the mood established at the hearings, however, I would expect, at the next briefing in a week or so, that he would state he had been ordered not to answer certain questions, or that he had been told not to give his opinion. I leave the Congressional reaction to that as an exercise to the reader.
Additional confirmation hearings also may give some insight. GEN Abizaid is retiring as head of Central Command. According to Mike Wallace and Bob Woodward, he had had conversations with Rep. Murtha in which Abizaid described his position as close to Murtha's.
ADM Fallon has been nominated to replace Abizaid. Fallon is current head of Pacific Command; it is relatively rare for one regional commander to go to another regional command -- they tend to retire, take a senior post in Washington, or sometimes a special post such as NATO commander. Fallon is considered an expert in strike warfare, as would be needed for at least some operations against Iran.
I can see some very, very interesting confirmation hearings for him. As far as I know, the hearings have not yet been scheduled. They certainly might include direct questions about Iran and possibly conditional confirmation based on his reporting to Congress, in executive session, about plans to attack Iran other than in direct response to a serious attack.