Pittsburgh - The Rev. John Welch paused, dabbing at sweat on his receding hairline. Dapper in a double-breasted tan suit, he stood silent for a moment in the pulpit of the Bidwell United Presbyterian Church here, and then resumed speaking on a new topic. "God wants us to take preventive steps for our health," he exhorted. "Only when we are healthy can we help someone else." Raising his left arem heavenward, the minister said, "Lord, we have beennegligent of what you have entrusted us with." Then he told his followers to get their blood pressure checked right after the service, downstairs in the recreation hall, where nurses were waiting. It wasn't Mr. Welch's idea to lace his sermon with health tips. The move is part of a broad experiment led by the University of Pittsburgh that aims to erase the disparities in health care between the city's whites and blacks by the year 2010.