After the recent visits to Washington by the Palestinian and Israeli prime ministers, the conventional wisdom is that the "road map" for peace in the Middle East is on track. But progress is built on fragile foundations: the temporary ceasefire of extremist Palestinian groups. Israeli concessions on prisoner releases and checkpoints, while welcome, mask the reality that neither side is fully implementing its road map commitments.

Paradoxically, Israelis and Palestinians are united in their support for the road map - and in their conviction that it will not succeed. That is why both sides are, disturbingly, flirting with a plan B. Parallel to their discussions with the Palestinians, the Israeli government is building a "security fence", creating new facts on the ground that will make a deal more difficult to achieve. Among Palestinians, there is growing talk of returning to a one-state solution if, as they fully expect, the road map fails to lead to a viable Palestinian state. That would mean the Palestinians somehow turning their demographic advantage into political liberation inside a single, democratic Israeli-Palestinian entity. Both ideas are inimical to the road map and a recipe for endless cycles of violence. Without a mechanism to ensure momentum, the risk is that the current phase will be short-lived and that both sides will soon revert to the familiar pattern of violence and retaliation.

If the US, Europe and others want to maintain the momentum behind the road map, they will have to make a greater investment - politically and militarily. They should propose that a Nato-led security force moves into the West Bank and Gaza. The aim would be to shore up a fragile ceasefire, help to break the current impasse in the security negotiations and thereby unlock progress in other areas.

The Israelis say they will not pull out from all West Bank cities unless their security interests are guaranteed. By common agreement, the Palestinian security services are too weak and fragmented to do the job. But it is equally clear that unless the Israelis withdraw, the Palestinian leadership - already accused of doing Israelis' bidding - will not be able to crack down on extremist groups. That is why an outside force should take over positions from the Israeli army and make up for the clear lack of trust between the parties.

Nato has peacekeeping experience in Bosnia, Kosovo and Afghanistan. It is constantly looking for ways to prove its continuing relevance. The idea of a Nato-led peacekeeping force, once dismissed as ludicrously ambitious, is slowly gathering support. In the US, Senator John Warner, chairman of the armed services committee, is a leading if lonely advocate. Senior US officials, including at the National Security Council, are known to be supportive. Nato defence ministers discussed the proposals in Madrid last month. The Dutch government is keen, as are top Nato officials. Nato has already brought Israeli and Palestinian security officials to Kosovo to show them how a force would work.

Among European defence ministers there is some interest but also deep misgivings about the risks. This is understandable; but the Europeans should be more forward-looking. European pleas for a more active and even-handed US stance on Israel-Palestine are justified. But such arguments might carry greater weight if European governments showed they were prepared to support a settlement, not just with extra money but also with troops.

Some Europeans, including Dominique de Villepin, France's foreign minister, have argued that the EU should send peacekeepers to the Middle East. But Israel would never accept a Europe-only force. To be credible, it has to be a Nato-led force to which other countries contribute. In any case, getting Nato involved in Middle East peacemaking would be a triumph for Europe. It would show the alliance can reconcile European and American priorities and that Nato is as good at promoting peace accords as it is at cleaning up after US-led interventions.

Israelis want security but do not trust the Palestinians to achieve it. Palestinians want an end to occupation but lack the capacity and credibility to run their own affairs. The outside world is desperate to keep the road map. A Nato-led force may be the only way out. It would also help patch up the battered transatlantic relationship. If the US and Europe cannot agree to shore up a peace effort in a region of vital interest to both, what exactly is the relationship for?

The writer is senior fellow at the Centre for European Reform.

Centre for European Reform © CER 2003