Barack Obama is to step up pressure on Congress to act on gun violence by surrounding himself with schoolchildren from across the country when he unveils proposals on Wednesday aimed at preventing a repeat of the Newtown massacre.

Although Obama can take implement some measures almost immediately through executive action, these are limited in scope. The wide-ranging proposals he is looking for require legislation, but he faces opposition from Congress, particularly among Republicans, backed by the National Rifle Association.

By bringing schoolchildren to the White House press conference, Obama can tap into some of the emotion aroused by the Connecticut massacre in December that left 20 children and seven adults dead.

At a White House press conference Tuesday, the president's spokesman Jay Carney said: "I can tell you that tomorrow the president and vice-president will hold an event here at the White House to unveil a package of concrete proposals to reduce gun violence and prevent future tragedies like the one in Newtown, Connecticut.

"They will be joined by children from around the country who wrote the president letters in the wake of that tragedy expressing their concerns about gun violence and school safety along with their parents."

Carney said that three measures the president wants would require legislation: a ban on automatic weapons; a reduction in the size of magazines holding bullets; and the closure of a loopholes that allows the sale of weapons at gunshows without the same kind of background checks as required elsewhere. Carney said the press conference was scheduled for 11.45am.

A Washington Post/ABC poll published Tuesday showed that 52% of Americans say they support gun controls in the wake of Newtown.

Vice-president Joe Biden, who is in charge of a taskforce set up by Obama to look into gun controls, promised last Thursday he would make an announcement Tuesday about his recommendations. Instead, it he has left it to Obama to take the lead.

Briefing members of Congress on Monday, Biden told them he had sent Obama 19 proposals that the president could implement through executive action, including better federal data to track gun sales.

Democratic congressman Don Barber, who was among those briefed, told CNN on Tuesday that while much could be done through executive action, the most serious aspects of gun control could only be addressed through legislation.

"In order to do something significant, we are going to have to pass laws," said Barber, a former aide to congresswoman Gabby Giffords, shot in Tucson, Arizona, in January last year. Barber was elected to replace Giffords.

Obama has already said that he favours legislative action to reduce the size of weapons clips, in addition to an automatic weapons ban. The NRA will oppose such a move and is almost certain to be backed by Republicans, who have a majority in the House.

Congress passed just such a bill in 1994 but it was allowed to expire 10 years later.

The 19 measures may include tracking of gun sales, addressing violence in video games and providing schools with extra cash for security.

Biden, when drawing up recommendations to put to the president, spoke to the gun sellers, the NRA and video game manufacturers.