ROM an obscure office park in Chesapeake, Va., Ralph Reed and his comrades are plotting a revolution in American politics. The Christian Coalition and its 1.7 million members have already enmeshed themselves in the Republican Party the way labor once held sway over the Democrats. But political control, says the boyish Mr. Reed, is not their aim: They want to save the nation from ''moral collapse.'' Are their solutions good for America? In a Monitor interview, Reed discusses the ''faith factor'' in politics, his own life, and the warning he has for the Christian Coalition as it convenes today and tomorrow in Washington.