The best indicator of whether a force can take a city is the degree of isolation the attackers can impose upon the defenders. In a study of 22 battles [1], the attacker won every time the defender was totally isolated, and only 50 percent of the battles in which defenders were not significantly cut off, and those victories came at great cost to the attackers.
The next best indicator of whether a force can take a city is the size of the attack force relative to the defense force. At Khorramshahr, irregular Iranian forces were outnumbered 4:1 by regular Iraqi forces (five armored and mechanized divisions), and they still held the city for approximately 26 days.
CENTCOM attempted to isolate Falluja in March and April. The April Seige of Falluja resulted in stalemate. CENTCOM has attempted to isolate Falluja since October 14th.
The ratio of forces at Falluja is closer to 1:1 than 4:1.
In most cases [in the study of the 22 battles-for-cities] the time required for successful conclusion of an urban battle exceeded the initial estimates by a factor of two to three. Most city battles, if not decided within 30 days, are not won by the attacker. The April Seige of Falluja was just under 30 days.
The question to consider is the liklihood of outcomes that result in the modification of operational or strategic plans. It does not appear that the conditions are present for CENTCOM to control the duration of the fight. Therefore it does not appear that CENTCOM can determine, or stage, the supporting forces and resources critical to the success of an attack -- the logistics push system that runs from Kuwait to Camp Anaconda and then out to the battle staging areas around Falluja. Further, it does not appear that CENTCOM has the supporting forces and resources necessary to the protection of the theater logistics system, at the existing pre-attack loading, and prior to any increase in interdiction attempts by defending forces able to operate in the logistical "rear area".
If there are operational or strategic plans, they probably include the January elections to legitimize some post-caretaker government. The Association of Muslim Scholars has already taken a position on the elections question. They will boycott, removing the urban educated 15% of the population from some post-caretaker government's claim of legitimacy, without firing a shot.
Paul Bremer killed over 100 Americans, maimed another 800 Americans, and killed or maimed thousands of Iraqis, in the April Seige of Falluja. Independent of outcomes, and the outcome of that particular battle was a stalemate, a November Seige of Falluja cannot be presumed to have a high liklihood of being more favorable for the attacker.
The necessity for having no zones of alternate authority prior to holding "free elections" is politically determined. The liklihood of holding "free elections" within 90 days of initiation of a campaign to reduce a major city is also politically determined. The military experience is that the operational and strategic plans are probably compromised by imprudent assault.
[1] Aachen, Arnhem, Ashrafiyef, Ban Me Thout, Beirut Port/Hotel (I), Beirut 1982 (II), Berlin, Cherbourg, Hue, Jerusalem, Khorramshahr, Manila, Ortona, Quang Tri City I, Quang Tri City II, Seoul,
Stalingrad, Suez City, Tel Zaatar, Tyre and Zahle.