Government testing for residues of an herbicide that has been linked to cancer has been put on hold, slowing the Food and Drug Administration's first-ever endeavor to get a handle on just how much of the controversial chemical is making its way into U.S. foods. The FDA ... launched what it calls a special assignment" earlier this year to analyze certain foods for residues of the weed killer called glyphosate after the agency was criticized by the U.S. Government Accountability Office for failing to include glyphosate in annual testing programs that look for many less-used pesticides. Glyphosate is the most widely used herbicide in the world, and is the key ingredient in Monsanto Co.'s branded Roundup herbicide line. Several private groups ... have been finding glyphosate residues in varying levels in a range of foods. Earlier this year, one of the agency's senior chemists also analyzed glyphosate residues in honey and oatmeal and [found that some] samples contained residue levels well over the limit allowed in the European Union. The agency ... put the glyphosate residue testing part of the work plan on hold amid confusion, disagreement and difficulties with establishing a standard methodology to use across the agency's multiple U.S. laboratories, according to FDA sources. With the testing on hold, it is not clear when the agency might have final results on the glyphosate residue analysis.