Speaking Softly In the Bully Pulpit
Pres Clinton, on eve of his second inaugural, is studying second-term inaugural addresses of Presidents past and thinking about junctures in American history when a leader helped transform the nation; he has turned for inspiration to Theodore Roosevelt, saying his speeches moved the country into the future; Roosevelt has many points of appeal for Clinton; he made powerful use of what he called the President's 'bully pulpit,' and Pres Clinton, faced with Republican Congress, has become more interested in oratorical potential in his office; photos (M)