Unhappy with some of the findings of the scientific advisory committees that guide federal policy, the Bush administration has begun to stack the deck in its favor, eliminating some committees entirely and reshuffling membership in others. Fifteen of the 18 members of a committee assessing the effects of environmental chemicals on human health have been told they will be replaced, in several instances by people tied to the industries that manufacture the chemicals. (One new member, a California scientist, helped defend Pacific Gas and Electric Company against Erin Brockovich.) Two other committees — one recommending increased oversight of the lucrative genetic testing industry and the other rethinking federal protections for human research subjects — have been eliminated. The changes mark the beginning of the restructuring of a system of more than 250 committees that funnel advice to Health and Human Services Secretary Tommy Thompson.