AZ ZUBAYR, Iraq — Iraqi leaders condemned Britain’s decision to withdraw troops, saying yesterday that it would lead to a bloodbath and ethnic cleansing.

After the Daily Telegraph reported that troop numbers would be reduced by between 3,000 and 4,500 at the end of May and withdrawn to a single base outside Basra, local party chiefs were shocked to discover that they were about to be abandoned.

They asked that Prime Minister Blair keep British troops in the towns to prevent the slaughter and forced expulsion of thousands of Sunnis, the minority in the Shiite-dominated South. Mr. Blair has promised that Britain would never leave Iraq “until the job is done.”

The town of Az Zubayr is unique in Iraq in that its 60,000 Sunni residents live in harmony with the 460,000 Shiites. People from the two Islamic branches live next door to each other, a state of affairs unthinkable in Baghdad. “The decision to withdraw is wrong and the British have the responsibility to protect us,” Sheik Abdul Kareem Al Dusari said. “The situation in Az Zubayr is good now because the rogue militias are asleep, but if the British leave, they will awaken.”

The leader of the Sunni-dominated Iraqi Islamic Party said Shiite militias planned to plant car bombs in Shiite areas and blame the killings on Sunnis.

That would create an excuse to attack them and effectively lead to Basra province being ethnically cleansed, he said.

Already the Sunni population in the province has dropped to 200,000 from 500,000 since the invasion of 2003 with many fleeing Iraq or joining their fellow believers in central Iraq.

Sheik Kareem believed that the militia were entirely backed by Iran, which wanted to dominate the area.

“I request the British people and commanders to keep British forces working in Az Zubayr until the Iraqi security forces have the authority to run affairs,” he said. “If I inform the Sunni people of Az Zubayr that the British are leaving, they will leave, too.”

He said that once the militias became aware that the British were leaving, they would move into Az Zubayr to overrun the police.

The sheik’s pleas were even echoed by the rival Shiite-backed Tharallah Party. The party leader in Az Zubayr, Salan Maki Mohana, said it would be “very dangerous” for the British to leave.

“Lots of people will take advantage of the bad security,” he said.

The Army had brought some major beneficial projects to the town including its hospital, schools, water, and electricity, he said.

At the end of last year, Muthanna province was handed over to local Iraqi control, but since then, the area had come under the sway of militias.

Similarly the volatile town of Amarah, which the British pulled out of in October, has now become a “no go zone” under the sway of the dominant cleric Moqtada al-Sadr, the fundamentalist leader of the major Shiite party.

There are fears that the same will happen to Basra province if the British pull back to the base five miles outside the town in June.

“If the British leave this area there is no security because security depends absolutely on them,” the local council leader, Moslem Hussayn, said.

“I am the democratically elected chairman of the town council, and I call on the British government to keep her forces working in Az Zubayr. We need them here until the Iraqi security forces are fully qualified for at least two years.”