The nation's Republicans are working against the clock to answer two key questions: Can conservative Ronald Reagan possibly attract enough independent and Democratic votes to win in November? "Reagan is the opponent of choice for Carter," says I. A. Lewis, director of the Los Angeles Times Poll, a point on which most analysts agree. "But Reagan can reach across and cause mischief in the Democratic constituency," Mr. Lewis says. "Reagan appeals to blue collar, working-class voters. He can win Democratic votes..."