The problems lie in the many variables and their logistical consequences.
NATO has in its own right, or through its member states, a large number of ways of ensuring an aerial exclusion zone in the skies over Libya.
There are AWACS (airborne warning and control system) aircraft to monitor air and sea space; electronically-equipped warplanes to neutralise ground-to- air defences; and fighter-bombers to intercept Libyan aircraft violating the no-fly zone or to destroy ground-to-air missiles.
To confront this western show of strength, Libya has only 20 or so old Soviet (Mig 21 and 23) or French (Mirage F1) fighters that are fully operational and have trained pilots.
The greatest danger comes from Libyan mobile ground-to-air missile batteries, either SA8 at low levels (5,000 metres, 16,000 feet) or SA2 and SA6 batteries at higher altitudes (7,500 to 8,000 metres, 24,600 to 26,250 feet).
The SA8 in particular, with its radar command guidance, follows its targets with a missile guidance radar that makes elctronic countermeasures difficult.
They constitute enough of a threat for NATO to need at the outset of the operation to carry out a preventive strike against the batteries with a risk of casualties among their Libyan operators.
Everything will depend on how much of Libya, a country of a million square kilometres, the no-fly zone seeks to cover.
Since 85 percent of the population live in a band 100 kilometres (62 miles) deep along the coast surveillance of that space might be considered sufficient.
The AWACS have an effective surveillance radius of 200 to 250 nautical miles (360 to 450 kilometres) at low level and so one of these aircaft stationed in southern Italy would be enough to cover an arc encompassing a good part of Libya, or at least the zone controlled by Moamer Kadhafi's troops.
It might not be necessary for the AWACS planes to fly at night as Libyan warplanes are probably unable to carry out night missions.
If the aim was to guarantee 24 hour surveillance five AWACS bases, for example, in Sicily would make in-flight refuelling unnecessary.
But if only three were used to save money, tankers would be needed, which would involve a considerable and expensive extra commitment.
If, in addition to this surveillance, the allies needed fighters with a capacity to intercept Libyan aircraft within five minutes more than 100 planes of all types would be needed to take part every day.
Assuming the interception time was extended to 10 minutes, several dozen aircraft would suffice. But that would give Kadhafi's air force a slight chance of striking their target before being shot down.
Accordingly countries ready to intervene need to define from the start how watertight an exclusion zone they want, what kind of mission they are undertaking and what the rules of engagement are before deciding on the dimensions of the operation.