By Phil Stewart WASHINGTON (Reuters) - The United States is **t preparing to unleash a "shock and awe" campaign of overwhelming airstrikes in Syria against Islamic State fighters and instead envisions a more modest, longer-term campaign, Pentagon officials told Congress on Tuesday. Defense Secretary Chuck Hagel said the military's current plan would be outlined to President Barack Obama on Wednesday by the U.S. military's Central Command and envisioned striking the group's safe havens to k**ck out infrastructure, logistics and command capabilities. General Martin Dempsey, the top U.S. ...