When a federal panel recently recommended against prostate cancer screening for most men, it tried to steer clear of any suggestions of commercial bias. All 16 members of the United States Preventive Services Task Force were vetted to ensure they had no financial conflicts that would prohibit them from voting, according to the panel's vice chairman, Dr. Albert L. Siu. But three other federal panels that are quietly developing major public health guidelines on the leading causes of cardiovascular disease — hypertension, cholesterol and obesity — operate under less stringent ethics recommendations. And one potential conflict after another has surfaced among the members, with some receiving speakers' fees from drug companies, others consulting for pay and others doing company-financed research.