WASHINGTON, Jan. 13 — Administration officials say they are planning an extensive election-year initiative to promote marriage, especially among low-income couples, and they are weighing whether President Bush should promote the plan next week in his State of the Union address. For months, administration officials have worked with conservative groups on the proposal, which would provide at least $1.5 billion for training to help couples develop interpersonal skills that sustain "healthy marriages."The officials said they believed that the measure was especially timely because they were facing pressure from conservatives eager to see the federal government defend traditional marriage, after a...