Private humanitarian relief groups are moving from city to city in southern Iraq for the first time since the war began, delivering medical supplies and preparing base camps as the impoverished region's security situation continues to improve.

Small teams are working independently of military forces and ahead of the United Nations, which has not yet declared Iraq safe enough for its staff to spend nights there. The aid groups' new efforts remain modest, but specialists hope they represent a growing momentum after weeks of idleness.

"It's safe to say things are picking up," said Michael Kocher, a staff worker with the International Rescue Committee, upon returning from trips to five southern cities. But he cautioned that Iraqi "expectations are high. There's a grace period that's available to the international community, during which they've got to produce. If they don't, the welcome is going to wear thin."

Conditions remain bleak across the region, and large-scale aid projects that Bush administration officials hoped would be underway are developing slowly. Meanwhile, a senior U.N. official, Kevin Kennedy, told aid workers here that while relief efforts have begun, the U.N. role in Iraq remains unclear.

Many aid groups and donor countries, reluctant to be tied too closely to the U.S. and British militaries, favor a coordinating role for the United Nations. They believe a U.N. umbrella would add legitimacy to the postwar effort and encourage wider participation. But many U.S. policymakers doubt the United Nations' abilities and are reluctant to surrender any authority.

For now, U.N. officials are planning to establish a string of regional relief offices in Iraq when conditions permit.

Experienced relief workers have reported that Iraq is not facing the humanitarian crisis that many of them feared before last month's invasion. The war has sparked neither hunger nor exodus so far, but Iraqis and foreign relief specialists warn that hardship is widespread, with electrical blackouts and water shortages posing serious health threats. Aid workers report that Iraqis have enough food to stretch for several more weeks, following the delivery of extra rations before the war. Markets are reopening, although money to buy the produce now for sale is limited. Relief staffers say it is important to restore a national food distribution system, which was interrupted by the war.

"Food is not an issue, but it is going to be," said a spokesman for Save the Children, Nicole Amoroso, on returning today from Basra. "What we need to do is make sure there is a system in place before you get to June. It has to be in place before people run out."

Iraq's national distribution system was run by Iraqis under the oversight of the U.N. World Food Program because of international sanctions that followed the Persian Gulf War. More than 60 percent of the country's population depended on the deliveries of such staples as flour and cooking oil. With the fall of Saddam Hussein's government, the World Food Program will work to get the system running again, an enormous challenge.

U.S. aid officials say they have been deterred by violence. Snipers fired on two top U.S. government health officials last week as their armored vehicles tried to reach a hospital. Conditions remain too risky in central Iraq for the U.S. Agency for International Development to send assessment teams, although the teams are now operating in northern and southern Iraq.

"There's still a lot of bad guys out there," lamented one official, who said the Americans understand that pressure is increasing to produce the results they promised in prewar leaflets and ongoing broadcasts. "It's tense inside Iraq," a senior official said. "These are people with high expectations that are not being met. The longer the water is off, the longer the electricity is not flowing, the more this will breed resentment."

On the bright side, U.S.-funded groups such as Save the Children and the International Medical Corps, as well as UNICEF, have begun doing more in southern Iraq, from resupplying looted hospitals to helping to arrange water deliveries. International Medical Corps doctors delivered supply kits and tested for the cause of a diarrhea outbreak in one town.

"Our reception in all of the places so far has been very welcoming. We have not felt any kind of security threats or hostility," said the International Rescue Committee's Kocher. "They were happy to learn we were not soldiers or media."

Sgt. Michael Bush of the 101st Airborne Division hands medical supplies to health clinic workers in Baghdad last week. The U.N. has not yet declared Iraq safe for its aid workers.