WASHINGTON -- President Barack Obama will launch the nation's most sweeping effort to curb gun violence in two decades Tuesday, setting up a legislative fight with a deeply divided Congress that even some of his staunchest allies expect to fall short of its goals.

The package Obama will announce, just over a month after the Newtown, Conn., school shootings shocked the nation, is expected to include more than a dozen steps the president can take on his own through executive action.

Those measures will provide a pathway for skirting lawmakers who oppose gun control, but they will be limited in scope, and in some cases, focused simply on enforcing existing laws.

The proposals that require congressional approval will include a ban on military-style assault weapons and high-capacity ammunition magazines, along with universal background checks on gun buyers.

Obama will announce his proposals flanked by children who wrote to him about gun violence after the massacre of 26 people at Sandy Hook Elementary School.

Some gun control advocates worry that opposition from Republicans and conservative Democrats, and the National Rifle Association, to some measures will be too great to overcome.

"We're not going to get an outright ban," Rep. Carolyn McCarthy (D-Mineola) said of limits on assault weapons. Still, McCarthy, a leading voice in Congress for gun control, said she would keep pushing for a ban and hoped Obama would as well.

White House officials have emphasized that no single measure -- even an assault weapons ban -- would solve a scourge of gun violence across the country.

The president's framework is based on recommendations from Vice President Joe Biden, who led a wide-ranging task force on gun violence.

Beyond the gun control measures, Biden also gave Obama suggestions for improving mental health care and addressing violent images in video games, movies and television. The vice president's proposals included 19 steps that could be achieved through executive action.

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Obama may order the Justice Department to crack down on people who lie on background checks; only a tiny number are prosecuted now. Such a step has support from the NRA.

He also could order tougher penalties against gun trafficking and give schools flexibility on grant money to improve safety.