Consider the Taco Bell steak quesadilla, with cheddar, pepper jack, mozzarella and a creamy sauce. “The item used an average of eight times more cheese than other items on their menu,” the Agriculture Department said in a report, extolling Dairy Management’s work  without mentioning that the quesadilla has more than three-quarters of the daily recommended level of saturated fat and sodium.

Dairy Management, whose annual budget approaches $140 million, is largely financed by a government-mandated fee on the dairy industry. But it also receives several million dollars a year from the Agriculture Department, which appoints some of its board members, approves its marketing campaigns and major contracts and periodically reports to Congress on its work.

The organization’s activities, revealed through interviews and records, provide a stark example of inherent conflicts in the Agriculture Department’s historical roles as both marketer of agriculture products and America’s nutrition police.

In one instance, Dairy Management spent millions of dollars on research to support a national advertising campaign promoting the notion that people could lose weight by consuming more dairy products, records and interviews show. The campaign went on for four years, ending in 2007, even though other researchers  one paid by Dairy Management itself  found no such weight-loss benefits.

When the campaign was challenged as false, government lawyers defended it, saying the Agriculture Department “reviewed, approved and continually oversaw” the effort.

Dr. Walter C. Willett, chairman of the nutrition department at the Harvard School of Public Health and a former member of the federal government’s nutrition advisory committee, said: “The U.S.D.A. should not be involved in these programs that are promoting foods that we are consuming too much of already. A small amount of good-flavored cheese can be compatible with a healthy diet, but consumption in the U.S. is enormous and way beyond what is optimally healthy.”

The Agriculture Department declined to make top officials available for interviews for this article, and Dairy Management would not comment. In answering written questions, the department said that dairy promotion was intended to bolster farmers and rural economies, and that its oversight left Dairy Management’s board with “significant independence” in deciding how best to support those interests.