Filed at 5:36 p.m. ET

WASHINGTON (AP) -- The Institute of Medicine is backing away from its conclusion last year that the children of veterans exposed to Agent Orange may have an increased chance of leukemia.

The institute, part of the National Academy of Sciences, concluded Wednesday there is not enough evidence to establish a connection between exposure and development of acute myelogenous leukemia. This finding came after researchers reviewed additional data, including a corrected Australian study.

``Obviously we're disappointed,'' said Len Selfon, director of veterans benefits programs at Vietnam Veterans of America. ``We'll have to see what they based the retraction of their original conclusion on.''

Veterans Affairs Secretary Anthony J. Principi said that for now, ``the scientific evidence doesn't support'' a connection. He said he would support benefits for these children ``if future studies reach the legal threshold.''

The institute reported last April that it had reviewed available studies and concluded that the children of veterans exposed to herbicides such as Agent Orange seemed to have an above average chance of developing that form of leukemia.

While the relationship between Agent Orange and various illnesses has been debated for years, that was the first scientific connection between the childhood disease and the pesticide. The finding stopped short of saying the link was conclusive.

In the new analysis, the researchers said an Australian study that was a major factor in their earlier conclusion had an error ``that led its authors to incorrectly conclude that these children faced significantly greater risk of AML than the general population.''

When revised, that report found that the incidence of the disease among the children of exposed veterans was slightly elevated, but within the range of normal variation.

In addition, the panel said it reviewed two small studies of pesticide exposure from Norway and Germany that had not been included in the earlier analysis.

``Our review of available studies, combined with the revised analysis from Australia, indicates that the evidence is too weak to draw any conclusions or even make tentative ones,'' said Irva Hertz-Picciotto, professor of epidemiology at the University of California, Davis, who headed the panel.

The report is the most recent in a series by the institute looking at the effects of the herbicides used in Vietnam.

During the Vietnam War, thousands of veterans were exposed to Agent Orange, a defoliant used to clear areas of jungle so the Viet Cong could be seen and attacked from the air.

Acute myelogenous leukemia is a fast-spreading form of leukemia that originates in bone-marrow cells. It accounts for nearly 700 cases of cancer annually among children under 15. It is also known as acute myloid leukemia and acute nonlymphocytic leukemia.

Previous studies evaluated by the institute have found suggestive but not conclusive evidence of a link between herbicide exposure and respiratory cancers, prostate cancer, type two diabetes, spina bifida in children and other conditions.

The National Academy of Sciences is an independent organization chartered by Congress to provide scientific advice to the government.

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On the Net:

Institute of Medicine: http://national-academies.org

Department of Veterans Affairs: http://www.va.gov

Vietnam Veterans of America: http://www.vva.org

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