Agriculture Secretary Edward T. Schafer is preparing to walk into a buzzsaw of criticism over American biofuels policy when he meets with world leaders to discuss the global food crisis next week. Mr. Schafer took the offensive at a press conference on Thursday that discussed the food summit, planned for Rome. He said an analysis by the Agriculture Department had determined that biofuel production was responsible for only 2 to 3 percent of the increase in global food prices, while biofuels had reduced consumption of crude oil by a million barrels a day. "We think that policy-wise in the United States of America