GENEVA, May 23 (Reuters) - Most Iraqi children have suffered trauma in the four years since U.S.-led forces invaded their country, and few are getting the help they need to cope, the United Nations said on Wednesday.

The U.N. children's agency UNICEF said insecurity in Baghdad and elsewhere in Iraq had closed schools and made clinics and hospitals hard to reach, causing immunisation rates to fall.

Only 30 percent of Iraqi children can access safe drinking water, with crumbling sanitation systems raising the threat of water-borne disease such as cholera, it said.

Iraq reported its first suspected cholera cases of 2007 last week and diarrhoea, the second-highest cause of child illness and death in the country, is also on the rise, UNICEF found.

Suicide attacks, bombings, kidnappings and other fighting between armed forces and sectarian groups have also claimed the lives of many parents, leaving children prone to abuse and exploitation, according to the report.

"Every day, more and more children are losing family members, friends and neighbours, school days, their health, their hopes, even their lives," it said.

"Most children have experienced trauma but few receive the care and support they need to help them cope with so much chaos, anxiety and loss."

Children make up about half of the 4 million Iraqis who have fled their homes since the 2003 U.S.-led invasion and overthrow of Saddam Hussein, which has unleashed deep tension in the oil-producing country. A spike in sectarian violence since last year has put Iraq on the brink of all-out civil war.

Of those uprooted by conflict, some 1.9 million people have stayed within Iraq, straining communities where schools are overcrowded and housing is hard to find. Another 2.2 million have gone to Jordan, Syria and other neighbouring states, and many are poor or living on meagre savings, UNICEF said.

"Refugee families, particularly those headed by women, are seriously struggling and a growing number of children are now out of school and into work, threatening their childhood and exposing them to potential abuse," UNICEF said.

UNICEF, which has received $20 million of the $80 million it is seeking for projects in Iraq this year, estimated it would cost $42 million to meet the urgent needs of Iraqi children in the next six months.

Its most important priorities include ensuring Iraqi children can access schools and health care and to protect them from exploitation, the agency said.