London - YESTERDAY’S announcement by Prime Minister Tony Blair that Britain will cut its troops in Iraq by 30 percent over the next six months and perhaps fully withdraw in 2008, followed by the news that the Danish contingent is also heading home, may seem like the death knell of the so-called coalition of the willing and a severe blow to American hopes.

Still — and I am well aware of how unpopular the presence of British troops in Iraq is among his electorate — Mr. Blair’s decision may have as much to do with strategic good sense as it does with domestic politics.

The truth is that the British gave up trying to win their war in southern Iraq a long time ago, and they probably accomplished as much as they could. Contrary to the grumbling among many Americans, they have done a lot of good work in southern Iraq. I have seen British troops on patrol in the marshes and countryside, watched grateful Iraqis rush to ask for their help in mediating tribal disputes or providing more protection from the militias.

Thanks to British oversight and protection, Saddam Hussein’s cruel efforts to drain the country’s southern marshes have been completely reversed. The marshes are now back to about 40 percent of their original size, with parts visibly flourishing. (With 75 percent of the water of the Tigris and Euphrates Rivers now siphoned off by neighboring countries before it gets to Iraq, it is unlikely that the marshes will ever recover fully.)

When I visited a date palm plantation near Basra last year, Iraqi farmers told me that British aircraft had sprayed almost 100,000 trees with insecticide, helping their production to double since the days of Saddam Hussein’s rule. (One of the men also insisted that I visit the old British cemetery in Basra. It was beautiful, he said: a sanctuary, a paradise. “And the gravestones are safe,” he assured me. “I have removed them, so no one will destroy them.”)

The British successes have also been political. In the south, Iraq’s elections and constitutional processes have been far more successful in terms of security and turnout than almost anywhere else in the country. There was never a popular uprising against the British presence.

True, after the Coldstream Guards stormed a Basra police station in 2005 to free two special operations troops being held captive, a photograph of a guardsman on fire atop his armored vehicle led newspapers around the world, giving the impression of a city and a region in flames. But the reality was quite different: that day, the angry crowd numbered only 200 — this in a city of two million, after two years of war.

Even over the last 12 months, the British military posture in the south has not been as passive as has widely been perceived outside of Iraq. One night last December, in a successful effort to capture weapons caches and terrorist leaders, more than 1,000 British troops in Basra, using high-speed landing craft and dozens of armored vehicles and tanks, carried out the largest coalition “strike operation” since the invasion.

But despite these successes, it seems the British never intended to “win” the war in southern Iraq. The British withdrawal from Iraq began almost immediately after the invasion. The British presence in the south, which was 46,000 troops in April 2003, has been under 10,000 since May 2004.

Unwilling or unable to rid the streets and farmland of Maysan, Dhi Qar, Muthanna and Basra of the militias who are the main threats to order in the largely Shiite south, the British troops’ goal has been to keep a lid on things until they could leave. They have not had the resources or the mandate to win a war against either the Iran-backed Badr Brigades or the more nationalist Mahdi Army of Moktada al-Sadr. And if those rival Shiite forces were to begin a fratricidal conflict, there is little the Britons would be able to do to intervene.

Americans must bear in mind that the situation in the south is very different from Baghdad and the Sunni triangle. In bloody Anbar Province the game is changing, and an American presence is helping convince local tribes to turn against the bleak worldview offered by Al Qaeda. In Baghdad, residents frequently express a wish for the Americans to return after they have declared a neighborhood cleared and moved on (as the current initiative in the capital is supposed to do). But there is no large constituency in Basra calling for the British to stay in force.

The “moral hazard” argument — the idea that the longer coalition troops stay, the longer we simply allow the Iraqis to avoid sorting out their own problems — is perhaps the most powerful claim for coalition troops to leave Iraq altogether. To some extent this is too simplistic: in Baghdad and the Sunni Triangle, the problems are too severe to be left to the country’s nascent security services immediately. But in the Shiite-dominated south, the centrifugal forces are less threatening than anywhere else.

Iraq’s historical state is one of constant internal violence. It is also, contrary to the claims of those who feel the country is a false concept of Western imperialism, one of territorial integrity within the current borders, which existed for 400 years of loose federalism under the Ottomans.

The priority now is to give Iraqis the best possible conditions to achieve the best feasible Iraq: one that stays whole; suffers less internal violence than it has historically; is not a threat to its neighbors or the rest of us; and that through a few good internal examples and a modicum of representative government has hope and mechanisms for improving itself.

This is an approach that will have to be adapted to suit each region. And in southern Iraq, it seems clear, it is time for the Iraqis to succeed or fail on their own.