Democratic governments live and die by their credibility with those who elect them.

Credibility is more than just telling the truth. It is also having a convincing story.

Electorates want to know that governments not only have good, honest, intentions (which are essential but do not by themselves guarantee success), but that there are also reasonable chances of their proclaimed goals being attained at acceptable risk and cost.

This is never more true than in war, when the stakes are especially high.

Image is everything

Political leaders must look as though they believe in what they are doing as their public will quickly detect it when they do not.

Inside government, public opinion constitutes a day-to-day test of the reasonableness of policy.

Can we explain this easily and convincingly? If not, there is usually something wrong.

Having a good cause and acting within the letter of the law, while essential, is not enough.

To sustain support over time, government action needs also to be relevant and proportionate to its objective. Material damage and casualties must, for instance, pass the test of justification.

Coalition warfare complicates the task of communication. Nato governments have come together over Kosovo because they agree on fundamental objectives.

But there are real and legitimate differences between them on the right means to use and thus on operational detail - for instance, on the appropriate use of ground forces.

These differences cannot wholly be concealed from view and will be debated in public, with the evident risk of them being widened and entrenched.

Political settlement

Over Kosovo, everyone agrees that the military campaign is a means to an end and that the solution has to be political.

But when should diplomacy kick into process and how should a strategy be formulated which keeps the coalition together, attains the objective and convinces public opinion in Nato countries?

None of these component elements can be ignored without serious detriment to the others. Compromises are necessary to move policy forward, but they risk undermining the clarity of the public message.

The facts of life in democratic countries open up many points of leverage for Milosevic to try to exploit.

The extent of public knowledge about Nato's early interdiction strategy enabled him to move ahead of it by sending his forces to Kosovo while the talking in Paris continued.

Surprise, so crucial to military operations, was lost to Nato which found itself on the back foot.

Milosevic's method

President Milosevic

• has created a massive humanitarian crisis to complicate Nato's military task and to transfer the pressure of time to Nato's side
• has made ceasefire offers which he knows fall short of Nato's demands in the hope that they will open up tactical divergences between Nato governments and, by their seeming plausibility, tempt Western public opinion to press for an end to bombing
• tries to undermine Nato resolve by creating controversy over individual bombing incidents where he can.

Cynical opportunism of this kind is not open to Western democracies.

It is also difficult for them to achieve strategic penetration of public opinion in Serbia, indoctrinated as it is by the single permitted broadcasting system controlled by the State.

BBC World Service broadcasting is one of the few - and a very important - way of getting through.

But, in the battle for credibility, Milosevic increasingly faces the awkward reality that his policies and his domestic propaganda undermine his external diplomacy: Nothing more cements Nato governments together with their publics or alienates from him the rest of the world than his wholesale ethnic cleansing of Kosovo Albanians.

Nothing more damages his plausibility than his denial of this and his assertion that the refugees are only fleeing Nato bombing. Ordinary Serbs must increasingly be wondering why they are so isolated.

Nato faces a longer and more complicated campaign than it bargained for. But militarily, Milosevic cannot win.