House Democrats to unveil gun control package; mirrors Obama's By Thomas Ferraro and Richard Cowan WASHINGTON (Reuters) - Democrats in the House of Representatives will unveil a proposal on Thursday to combat gun violence, including a bid to ban assault weapons, party sources said. In addition to outlawing semi-automatic assault weapons and imposing limits on high-capacity ammunition clips, the House Democrat package, like one advanced by Democratic President Barack Obama, would require that all gun buyers be subject to background checks and provide for improvements in mental health services. All these proposals - except for those concerning mental health - will face obstacles in the Republican-led House. House Democratic leaders, joined by members of the chamber's gun violence task force, are planning to announce the package after a visit to their three-day retreat in Virginia by Obama, who has made gun control a top priority in his second term. The debate over gun violence gained urgency after a gunman killed 20 first-graders and six adults on December 14 at Sandy Hook Elementary School in Newtown, Connecticut. The killer, 20-year-old Adam Lanza, used a Bushmaster AR-15 type assault rifle to shoot his victims before killing himself. Vice President Joe Biden, who led the effort to craft the White House proposals, told House Democrats on Wednesday that they have an obligation to step up and take action. "I don't want to hear about 'well we can't take it on because it's too politically dangerous,'" Biden said. There's an overwhelming consensus about the need to act. Biden acknowledged that members of Congress who backed a 1994 ban on assault weapons - which expired in 2004 - faced a voter backlash that may have cost many of them their jobs. "I'm here to tell you the world has changed since 1994," Biden said. A bipartisan group of senators on Thursday offered legislation expanding access to mental health professionals and improving the quality of mental health care in the United States. The group, led by Democratic Senator Debbie Stabenow of Michigan and Republican Senator Roy Blunt of Missouri, noted that people experiencing severe but undiagnosed psychological disorders are at risk of committing violent acts at a rate 15 times higher than those receiving treatment. The powerful National Rifle Association has led the charge against stricter gun laws, but has agreed with those who have called for improvements in mental health treatment. At this point the only gun-related proposal with much bipartisan support is the one requiring background checks for all gun buyers. Reporting By Thomas Ferraro; Editing by Xavier Briand