WASHINGTON (AP) - Braced for a fight, President Barack Obama on Wednesday unveiled the most sweeping proposals for curbing gun violence in two decades, pressing a reluctant Congress to pass universal background checks and bans on military-style assault weapons and high-capacity ammunition magazines like the ones used in the Newtown, Conn., school shooting.

A month after that horrific massacre, Obama also used his presidential powers to enact 23 measures that don't require the backing of lawmakers. The president's executive actions include ordering federal agencies to make more data available for background checks, appointing a director of the Bureau of Alcohol, Tobacco, Firearms and Explosives, and directing the Centers for Disease Control to research gun violence.

But the president, speaking at White House ceremony, acknowledged the most effective actions must be taken by lawmakers.

"To make a real and lasting difference, Congress must act," Obama said. "And Congress must act soon."

Obama vowed to use "whatever weight this office holds" to press lawmakers into action on his $500 million plan. Still, even supportive lawmakers say the president's proposals - most of which are opposed by the powerful National Rifle Association - face long odds on Capitol Hill.

The president was flanked by children who wrote him letters about gun violence in the weeks following the Newtown shooting. Families of those killed in the massacre, as well as survivors of the shooting, were also in the audience, along with law enforcement officers and congressional lawmakers.

"This is our first task as a society, keeping our children safe," Obama said. "This is how we will be judged."

The president based his proposals on recommendations from an administration-wide task force led by Vice President Joe Biden. His plan marks the most comprehensive effort to address gun violence in more than two-decades.

The president is asking Congress to renew the ban on high-grade, military-style assault weapons that was first signed into law by President Bill Clinton in 1994 but expired in 2004.

Other measures before Congress include limiting high-capacity ammunition magazines and requiring background checks for all gun buyers in an attempt to close the so-called "gun-show loophole" that allows people to buy guns at trade shows and over the Internet without submitting to background checks.

Obama also intends to seek confirmation for B. Todd Jones, who has served as acting director of the Bureau of Alcohol, Tobacco, Firearms and Explosives since 2011.

The president's long list of executive orders includes:

- Ordering tougher penalties for people who lie on background checks and requiring federal agencies to make relevant data available to the federal background check system.

- Ending limits that make it more difficult for the government to research gun violence, such as gathering data on guns that fall into criminal hands.

- Requiring federal law enforcement to trace guns recovered in criminal investigations.

- Giving schools flexibility to use federal grant money to improve school safety, such as by hiring school resource officers.

- Giving communities grants to institute programs to keep guns away from people who shouldn't have them.